Scanmaster, Turbolink and DirectScan are the most popular scantool devices for these cars, and actually geared towards them.
Scanmaster gives you all the info you need, easy to hook up and very convenient because of its size + you leave it hooked up (nice to not have to carry around laptop all the time). If you have a laptop then consider the Turbolink program or Directscan.
IMO it is best to upgrade to the '86/'87 ECM which makes available more info, and to use the Scanmaster it is a prerequisite.
Do searches on these three scantools to find out more opinions/comments and info. Both on this site and gnttype.org plus here ya go:
FULL THROTTLE SPEED - Item Description Page
TurboLink™ - A Brain Scan for Your Vehicle!
Chu Engineering Home Page
The one in the link you posted is a good scantool geared towards a mechanic and is good to have if you are going to be working on other OBD1 vehicles. The ones I mentioned are geared towards Turbo Buicks and [I would say more user friendly] towards tuning these cars. I have a general scantool much like the one in your link that I use to check vehicles Im working on, but when it comes to the Buicks it does not compare.
I currently use both Scanmaster and Turbolink on my cars. Scanmaster for everyday and TLink when I get a little more serious with recording, etc on the street or at the track. Seems that Directscan [although not as visually pleasing as TLink] is the choice of the big racers. LOTS of info and not fed of the ALDL like the other two but rather directly tied in at the ECM, so quicker read.
Good luck.
P.S. Forgot to mention Turbolink does work on other vehicles also. Also dont forget to check the For Sale forum. Someone usually has a deal on this stuff.