The one Rimmer's are selling is now likely to be a Ti pump as X-part now only supply these as opposed to the Pierburg
They are good quality and should be reliable if you have a look on eBay you should be able to find a genuine one a little cheaper.
There are cheaper pumps available but can be unreliable even from "trusted" sources.
I've seen one that lasted 2 hours, it was guaranteed but that's not much good when it fails and leaves you stranded
Russ