The Bearcat 300 had service search with a dedicated button for each service, while the Bearcat 250 did not have service search at all. I think that is the main difference in the feature set.
They were both plagued by cold solder joints and other maladies common to the Electra Bearcats. Uniden did continue producing the 300 after they bought the Bearcat line.
A buddy of mine had one back in the day - simply a great scanner, one of the best Uniden has ever made. It was extremely sensitive, even picking up low band skip on the stock antenna. (this was during Cycle 22, early 90's)
As for the SDS-250, a great feature to include would be a detachable head.