We had a microchip placed in our Great Dane when he was a pup. That gave me great peace of mind b/c most vets nowadays, at least in the Chicago area, will scan all new patients. The problem with the SNAGG product (no disrespect to them) is that it doesn't function like a LoJack or GPS. The instrument, unfortunately can't be tracked. You are relying on the shop where the stolen instrument is to be sold to have the scanners available. This breaks down for at least 2 reasons. First of all, I doubt most, if any, pawn shops have the technology and no guitar retailer I've ever seen has it either. They simply check serial numbers - if that. I'm sure if you're bringing a '65 pre-CBS strat to George Gruhn's store, he'll be scanning away. But Guitar Center isn't.
Second, I doubt that most guitar thieves are selling through normal channels, anyway. Unless you consider the trunk of a '78 Buick a normal channel. And, if they keep it for themselves, all bets are off.
Alas, while the microchip idea sounds great, I doubt that it is very practical for our beloved Alembics. Having them well insured is probably the best recourse.
Food for thought,
Jonathan