Before I realized that Snap-On might only have engine and trans capability, I recommended them based upon the fact that although a new unit cost about $4k, the older units will work just fine with all the vehicle specific modules like MB, BMW, and VW/Audi. The VW one is supposed to be the best thing I can have at any price. The BMW works on body and chassis functions. If the MB module only does eng/trans then it doesn't solve the MB problem!
The point to all ths was that OBDII is poor for eng diagnostics where it works (won't do anything on a pre 96 car, of course exceptions occur such as the MB C car) and absolutely useless on the many questions I read about here. Most of the repairs I do with a scanner are not engine related so an OBDII device is useless in those areas and poor everywhere else.
With that all in mind I figured that a used Snap-On would really offer a DIYer a usefull view at maybe double the price of some OBDII testers. (500 used and a MB module for 500 new or less used). As a 700-1000 tool the Snap-On was a good alternative, IF IT DID ANYTHING. I thought it probably did, but I might be wrong, I am just figuring it out.
There are a number of good alternatives that one could watch for. I got 1000 for my AST retriever with rather old software but fully functional to about 1998 (fully functional as aftermarket scanners were in 1998). I saw one on ebay a while ago that looked like 700 would take it.
There is a new tool out that costs $2400 that does real good on MBs and also just about everything else Asian or euro, see
www.x431.com . Most scanners cost more than that just for one application. A new Baum with best MB module is probably $4-5k
The AST is a little cheaper.
My original point to making the suggestion of a Snap-On was base on the never ending source of cheap used versions on ebay and the knowledge that anyone really interested in dealing with diagnostic code will be stopped real quick with only a OBDII device.
To me it is sort of like saying: Here I have a real good story for you. It is real expensive though and so I will sell you only page OBDII and you will have to dream up the rest of the story. Having just OBDII would be like only getting page 15 in the 10,000 page book of MB diagnostics. I think that it is important for me to impress upon those considering such tools my opinion of this relationship. I think one page out of 10,000 gives a good picture. It may be more accurate to say one page in a million.