Road & Track did an article on these chips (in general) several months ago. The consensus is that for any modern car they're a waste of money--not just the Probe. Off the top of my head, they tested a BMW 3-series, a 'Vette, a C/K-1500, a Ranger, I think a Viper, and a Lumina. Basically, a general cross-section of vehicles. They tried out all the major chip makers (Dinan, Superchips, etc.)
Not a single one produced any benefits at all. In fact, the Superchips in particular REDUCED hp & torque!!!
The only chip that made any difference was the tune-it-yourself one (I forget the manufacturer's name), and that was marginal & required scarifices in one place to get gains in another.
The upshot is, don't waste your money on chips, find another bolt-on.
'95 Black PGT -- work in progress (many mods, many to come)