Go for the second hand speedmaster from a reputable seller. This is the one you want and will eventually buy. If you really want to know more than you should about the watch, get the moonwatch only book. This is the bible that will help you to check everything from every version ever of the myth. Even if you don’t buy at the end, if you’re a geek I can assure you you’ll dig the content. The movements in those Tissot watches are crap, you’d be better get a serviced vintage in the 500-700 euros range than those glorified fashion watches in my opinion.
Interestingly, if you'd like to see a really cool site that showcases how these crap Tissot movements work, just click the link at the top of this page.
(The Powermatic 80 movement in the entry-level Tissot models is a modified version of ETA 2824 which Ciechanowski is showing on his site.)
Well, crap was maybe too strong of a word but they're nothing to write home about and not very precise (–4 to +10 seconds). OP seems attached to historical value, and if you ask me there's more interesting vintage watches to buy for that money, and some watches that will hold their value and aesthetics way more than PRX, which is all the rage now and will probably get old pretty fast.
Reliable pretty much yes; serviceable -- depends on your definition of that. For about USD 200, Tissot will take care of your watch and send it back to you in a working condition. Note that they will probably replace the whole movement. FWIW, Seiko will probably do the same "service" on their 4R/6R movements which are their "workhorses."
Huge fan of anything with the Powermatic 80. Mine gains about 3 seconds per day. I wear a Rado but I believe both Tissot and Hamilton also offer this movement.
