They stock a lot of components and spares but I've always found them expensive. For eg, the wheel bearings used on my trailer work out at nearly 50 quid a pop. In the packet are bearings made by SKF. The same SKF bearings from Parrymore are roughly half that price. Yet if I go to my local bearing and seals place I can get the same SKF bearings for half the Parrymore price.
When I priced up the suspension from Indespension it work out nearly double the price from Parrymores. The only thing that I didn't buy for my trailer refurb was the chassis, which is galvanized anyway. Got good service from the staines people who were very helpful and showed a genuine interest in what I was doing. Sorry to say that I didn't get the same impression from my local Indespension place. Sometimes the smaller companies go that bit further.
Like all things in this life, you makes your choice and pays your money.