Cross-posting and possibly (probably?) repeating myself...
I've had some time to live with the Rider 550. Long list of stuff follows:
I'm inclined to think corporate TomTom is, in its own way, about like Garmin to deal with. Specifically, there;s a user forum for TT products. Responses from TT support are ...ah... rare. There is only one way to get traffic and weather info to the 550: through the MyDrive app, which must be set to exchange anonymous (or is claimed) use info. More about MyDrive below. For some reason, the 550 doesn't display elevation data although it's inherent in all GPS fixes. Getting TT to at least actively look into this is... crickets, nothing but crickets. While the 550 supports a wide range of languages in voice prompts, very few languages included speak street names. Again, no comment from TT about this (even if it's just "we can't keep things correct" or whatever).
The MyDrive app, is needed to manage a BT link between the 550 and phone (phone then moves data in or out via its connection to the Internet). Pairing directly between the 550 and phone is a waste of time; the 550 won't move data through the pathway. MyDrive must have notification permission, access to the phone (of course), messaging (of course), and BT data transfer (of course). But if the user doesn't want to send anonymous usage data, traffic reporting, weather reporting, and avoidance aren't sent to the 550. In short, the user is coerced into using core features. But wait, it gets worse.
MyDrive under Android (I don't have iOS experience) is a major battery drain. And it can't be turned off or put into sleep mode. It launches at boot-up and stays there, even if the 550 is not even vaguely in range for the BT link. If MyDrive's on a phone and the 550 won't be used until the next weekend, tough. It's still there, draining the battery at a very high rate. There are two cures: uninstall the app (app-killing/stopping apps or settings do not work - MyDrive is "The App That Won't Die") or have a rooted phone capable of running Titanium backup app. The first route's obvious. The second route (no pun intended) is limited to a very small group. Rooting is never something for casual users - get it wrong and the phone can be bricked. Additionally, a large number of phones can't be rooted (thank you, US wireless company monopoly). Rooting is not the same as unlocking, BTW. However, Titanium can "freeze" almost any app (freeze the wrong app and the phone dies) including MyDrive. Reboot after freezing it and MyDrive ceases to exit until it's "thawed".
Attempts get TT to be a little(!) more user friendly, by adding an on/off option... crickets, nothing but crickets.
That's the bad news
The good news: This thing screams through data with a four core processor. The screen imagery is crisp (but why, why, why a glossy, sun-reflecting surface???). The touch sensitivity can be changed to allow use while wearing gloves(!). The type-in "keyboard" can be configured for bare fingers or clumsy gloves. The internal WiFi capability means there is no need for a wire connection to a PC for updates. TT recommends having power supplied to the 550 while updating.
For some reason, I couldn't sort out the "what maps and how much" and "how much for traffic" points. The answer is buying the 550 gives lifetime updates to what amounts to global mapping. Including "Oceana" which, I guess, means islands everywhere???. The full Europe map set and North America map set won't fit into the phone simultaneously. TT gives a good collection of European map subsets. Or the NA maps can be pulled to make room for all of Europe. Pull that set to make room for another set without worrying about "we gave you some maps and you tossed them? No reload for you". Traffic and weather data support is also a lifetime feature. The POI info is updated regularly.
Figuring out the on-board routing and other menu items is easier for anyone who hasn't used any GPS at all. For anyone else, there's a learning curve to undo old habits.
One the things I used to curse Garmin about is the voice prompts, via BT to a headset, were screamingly loud, with no volume control. Jump over this section if you don't care about BT and headsets. First, it turns out that the 660's link to the headset was only via HFP (hands free protocol - a BT protocol that's good for simple voice and minimal control activity). HFP is why MP3 playback on the Garmin 660 is so lame; it was never meant for music, ever. Also, HFP means any sound moved of an HFP link will always be EFFIN' LOUD!!
The TT 550 offers a work-around. The headset/intercom must support two BT links (not all do - Sena 20S and 20S EVO do, for example). Step one is pair the phone the headset. It's almost certain the link will use A2DP (the "hi-fi" link). Step two, pair the 550 and phone. Again this is almost certain to use A2DP. Step three is to pair the 550 with the headset. This is the place where the protocol is the 550 user's choice - use A2DP. With at least the Sena, music from the phone will be squelched or dropped under voice and beeps from the 550. Yea! There's still no volume control. Sorta. With the headset off (stops BT link), use the 550 volume control for speaker mode. Dropping to 20-30% should work. Turn the headset back on (BT between phone, headset, and 550) and the 550's volume is reduced! Woohoo! The 550 is that flexible.
The mount supplied with the 550 is a motorcycle mount with a RAM Mount ball on it. I have a RAM Mount mounting place design to replace the brake or clutch master cylinder. A short "dog bone" holds things together and allows positioning. The mount includes a two lead "pig tail" long enough to reach most batteries/distro boxes. The 550/mount interface is far more secure than the 660's. If the 550 pops off the mount it's because it was never put on correctly. The 550 must go downwards to lock, and can only unlock by pulling back a tab and sliding up. An add-on security lock (covers the release tab) is available for a silly price. Remove the 550 and hide it somewhere safe. There is also a car, suction cup windshield mount. It's got a clever way to get full suction. Plug a USB cable into the back and run it to a power point adapter. The adapter must have 2.4A capacity to keep the battery charging during use. The 1.1A port doesn't keep the battery "fed" during use.
Bottom line: would I buy it again? Yes. But I'd be more aware that TT doesn't listen well. The phone app is a necessary evil and PITA - without it not much useful happens. Drat.