Not to slam mechanics but many are not as electrically inclined as they should be. Special service tools like the checker are designed to both overcome that and to speed things up. The checker does make things easy but as a EE I can do pretty much anything the checker can do with normal test instruments. It does take a bit more time though. One nice thing about the checker is that, in addition to testing the car's sensors and wiring it can simulate them, thereby endowing the ability to test the ECU itself for problems.
The other reason I was thinking of selling it is because frankly my car never gives me any problem so I don't use it very often. I've always stayed on top of things in the electrical department and the car gets a full going over twice a year with all my other gear. And if something does act weird it's easier for me to break out the other test gear rather than pull the glove box to access the ECU for the checker to plug in.
The bottom line (and you already know this) is if you stay on top of things problems are rare. Unfortunately most of the guys who own the car bought it from people who either didn't maintain it properly or worse, hacked it up. Is the checker needed for the average guy? Probaly not unless he's limited in electrical ability, works on the car a lot, or runs a shop. I fall into none of those categories but have collected MK III stuff for 19 years in an effort to educate myself about the car. The checker was something I came upon that I couldn't turn down at the time.
Btw, the checker is capable of testing many other Toyota models. All that's required is the proper sub-harness for the vehicle. The MK III requires two, one for 88 and below and the other for 89 and above. I don't see them in that auction so they'd have to be ordered from Toyo. Finally I need to pint out the obvious: As with any peice of test gear the checker is not a substitute for knowledge.
Also, don't buy that thing just for the TCCS book. Be patient....if you get my drift
