OBD II Reader

I find occasional mention of OBD II readers or the lack thereof, but I don't see enough to get a clear impression whether there is a favorite. We have a 2007 9-3 Aero Sport Combi with a new (used) engine (long story) that has been coming up with engine lights *way* more frequently than the old engine. This might just be settling in and sorting things out, but it is quite annoying to feel like one can't safely drive the car until our very busy mechanic can look at it, especially since all he has done so far is to reset it. I know that the inexpensive readers aren't going to have the software to cover all the Saab-specific codes, but even if all we can get is a code to call in to the mechanic, we would know whether we had a problem or not. Are there sources for the codes on-line? It would seem very handy if the unit could do the reset, if we determined there was no real problem. Also, I am unclear whether these mass market readers can read history, i.e., if there is more than one code that has occurred. The one reader I have had someone recommend is the FIXD reader, https://getfixd.io/blog-students-vs-...vsl/?lpid=1346 , but she is not a Saab owner.