Are you saying that your interpretation is to do a maneuver that places an aspect for 3 shifts, then add 2 shifts for each added duration and free tag?
So... a 5 shift maneuver would give you 2 free tags for 2 rounds?
I just reread the rules and I had misunderstood stickiness as granting extra tags for each shift, which it doesn't do. So...oops.
So the only real thing you can do with Buffs from evocations or potions, is replacing a skill use with the effect OR granting aspects to yourself. Each aspect costs 3 + Exchange Duration in complexity. So with 6 Lore you could get two aspects you can tag for free and last 1 exchange or one aspect you can tag once for free and lasts 4 exchanges -- it's a bit unclear how to regard duration in a potion actually, as you could have it produce an effect that lasts a long time via thaumaturgy one would think, I was using the evocation rules. Seems like with items you can do better than that, so you can go with Thaumaturgy rules.
Hmm, it is actually unclear how this exactly works with Thaumaturgy. A navel-gazing maneuver is unresisted. Theoretically you could place a ton of "Deep Concentration" aspects on yourself with a potion (at least 1 per complexity) that can each be tagged once. The thaumaturgy section explicitly says you can put the same or similar aspects on a target and each can be tagged 1 for free -- it even suggests doing so. Thaumaturgy doesn't going over this sort of thing at all and the initial implications are that it offers something ridiculously OP. I'd suggest a navelgazing thaumaturgy maneuver needs 3 shifts (like an evocation) and lasts for the scene, until canceled our by another manuever, or until used. An additional shift can make it sticky (requiring a fate point to use after it is tagged and remaining for the whole scene). That, I think, prevents it from being horribly broken for items and potions.
I think the thaumaturgy section is what got things confused in my mind.
I think a Complexity 6 item or potion that gives you an aspect you can tag twice in a scene (technically it gives you the aspect twice) and then goes away feels right. I'm not 100% sure how balanced it is, but in normal games I don't think it is significantly unbalanced.