Can't quite see what the "/GE" is, but that looks like a regular AHA-2940, so narrow (8b), non-ultra (max 10MHz). The UW is both wide (16b) and ultra (20MHz), so is theoretically four times as fast. For the DVD it won't make a difference, for the HDD it might, depending on specs.
As for whether it's worth buying, that depends on price and what you want to do with it. For P166MMX, I'd aim for at least Ultra (AHA2940AU is ubiquitous) if not Ultra Wide (AHA2940UW). I'd also pair it with an UW HDD if possible, although actually I try to use Seagate Cheetah drives in as many of my SCSI builds as I can manage as they are very, very fast (low seek times) and - for SCSI - pretty quiet. They would be fastest with U2W SCSI (eg. AHA-2940U2W) in that system, but it really doesn't matter too much - the advantage of SCSI is low seek times and low CPU utilization. Linear transfer rates are less relevant - they matter for copying big files, but not for all the random reads when booting OS, for example.