It hasn't been an issue at all for me, GG, and no change of grip required (me). I'm still able to basically lay my thumb across, exactly as I normally would, and fire it.
That being said, since it's mobile use (mainly), I literally never use the lower buttons. I just tried them and had no problem, and I've got some fairly chubby thumbs. If one was inclined to constantly change settings and stuff though, I could see that as a potential issue, but it obviously isn't for me (since I've no such inclination).
The battery thing also isn't an issue for me since an 18650 carries me PLENTY long at my whopping 11w (of pure & unadulterated power). I usually remove the sleeve long before I need to swap batteries, and if I'm putting the sleeve on, I throw in a "freshie" anyways.
I decimated my V3 tube (and love it, all beat up and what-not), but I want to keep both Minis as pristine as possible. We've got ZapWrapz for when they begin to go, but the sleeve will keep that somewhere well down the line.
I use it with both the Purple and the Titan, and the impact to the finish has been zero (both, and to date). They still look flippin' awesome (IMO).
I absolutely love the sleeve, and will be
ever-appreciative of the (very unexpected) birthday surprise.
I expect you won't need to guess the source.