Not had my bike serviced at Bahnstormer yet, but their prices are more reasonable than some.
Their parts and accessories dept is good, you can usually badger them for some kind of discount and they hold a fair amount in stock.
The only Triumph dealer I've ever had dealings with is Haslemere Motorcycles. TBH, I had a less then stellar experience with them when the clutch on the 2nd hand KTM950 I bought from them was knackered. They sorted it all out eventually, but I really do think it should have been properly test ridden first before they put it out onto the showroom floor.
Mike