A Plitron is a standard transformer. But Bryston doesn't use Plitron exclusively. So if you want a Plitron, just ask them for one. It should make zero difference in sound or performance.
It's sort of akin to saying you want Michelin tires vs Goodyears when you buy a new car. The tires have the same specs, ratings, performance, warranty, etc, but you prefer one vs the other for your own reasons. The dealer is willing to accommodate.....so, why not? If it makes you feel better about your purchase, go for it. I probably would too, to be perfectly honest.