1. Yes, mechanical friction is indeed exactly the same one valid for a standard hub dynamo, both so far use bearings.
Friction is of course much better whether compared with bottle type or spoke dynamos
2. The advantage compared to a hub dynamo is that you don’t need to build a new wheel
3. Another advantage is that you can install one of them either on front or rear wheel, or on both wheels just in case you need more power
4. Might be available with different output rated powers just playing on number and strength of magnets and coils arrangement
5. Conversely among possible critical points and disadvantages I can see
- overall design that doesn’t allow for pole-claw configuration typical of hub dynamos
- total exposure to atmosphere
- requires accurate installation to reduce to a minimum the airgap in the between rotor and stator
- possible strong axial vibrations
- weight

In my prototype:
- the output power was pretty low, yet enough to light-on at very low speed some RGB leds
- rotor-stator airgap was very big
- magnetic circuit was extremely poor (I used a disk brake!!)
- coils were recycled junked relay coils

For the crowdfunding model/prototype you can visit SPINETICSINC