ASR10 is a totally processed radar which suffers from track jitter. I can see it's suitable for some airfields inside controlled airspace where you rarely need track accuracy or need to do SRA's, but the Watchman had better data presentation due to it's analogue type display, plus if necessary, you could cancel the AMTI and 'see' raw radar whereas the ASR10 signal is sent from the radar head to ATC in processed form. Also with Watchman, the track history was in the form of a tail formed from the afterglow of previous blips, with ASR10 it's formed by electronic trail dots which don't give you the same information.