A year or so ago, I specifically asked Doran if I could use their sensors on the Ariete aluminum valve stems (same as Bike Effects sells), and they said yes. However, the profile is too low and they won't work on Feej wheels very well.
Doran also says in their literature that comes with the kit, that their 90 degree metal stems are OK for internal or external mounting of the sensors. However, do not mount externally if your existing 90 degree stems have any kind of rubber on the stem, as they will eventually fail (and I know of those who have had that failure). Use the Doran 90 degree stems.
On the Feej, there is not enough clearance on the front wheel to mount the sensors externally, as they will be sheared off by the brake caliper, per my personal evaluation.
I have my front inside and my rear outside, and I did not use the silly "locks" on the rear sensor. The only danger with internal mounting is you must be careful when changing tires.