The Snap 3 Pro does work and sticks adequately to a naked base model phones. In most cases, the grip works just fine. However, it will not stick *as well* as if you used a case (non-silicon).
Snap 3 Pro is Apple MagSafe compatible, adhesive assisted. It's more difficult to remove than typical MagSafe accessories because you can use other MagSafe accessories on top of it and we don't want it coming off! The magnets inside your iPhone just aren't strong enough to keep Snap 3 on your phone if you stick it to a fridge or car mount.
The Snap 3 Pro is easy to remove with a credit card and easily reapplied repeatedly.