I recently purchased the Icarsoft MB 2 scanner for my ML550. Its very indepth and can give you want you need to know, but you need to know what to look for. Unlike many scanners advertised, it doesn't just spit out codes. You have to look through the menus to find them so its not terribly user friendly but it is effective. The price you pay for that inconvenience you get back through its depth of analysis. If you're an investigator and want to dig deep, it works. If you're looking for an easy answer to everything, maybe there are better ones out there. For the money, it exceeded my expectations and would recommend it but noting my comments. I was gladly surprised by its quality which was much better than expected. Some messing around with updates at the start but otherwise its good. Gives you live data on everything which can be a bit much as you need to be able to interpretate it.
I've never had a CEL so it could be more useful if that wasn't the case
Otherwise its totally compatible with my car and works seamlessly.