Good questions, Accomplice...
I have my doubts that TBT based antifouling will last any longer on your prop than the copper based ones. It will quite likely perform better as growth inhibitor while it lasts on the prop's surfaces, but my guess is that it will erode away just as fast as other paints.
We've been pretty happy with Propspeed ourselves. We bought enough for our prop from a friendly slipway for 30 AUD, and applied it according to instructions. Not at all difficult, despite what the 'authorized applicators" will tell you. It has been on for almost two years now, and is stilll somewhat effective. Not as good as when new, but growth still comes off with a gentle wipe with a green Scotchbrite pad.
I don't like Propspeed's business model... the common refusal to sell to DIY
applicators in much of the world. Around the parts
of Oz that we frequent those folks will charge upwards of 200 AUD for doing our small prop. This involves around 15 minutes of labour (plus some waiting for stuff to dry) and around 30 bucks worth of materials. I dunno if this is "fair" pricing for doing the job, but denying us the chance to DIY
But despite this disagreement with business practice, it is the best stuff we've found yet for keeping your prop clean!