I don't have a B28 but I do have a B30 in .22 that I tuned with James Maccari parts and I love it. It's averaging 765 fps with RWS Superdomes. I like the fact that it's fixed barrel, though mostly for looks. I like the fact that a bipod is easy to install on it, as are sling swivels. I polished the trigger parts and tuned it using a Maccari tune kit and seals for an RWS48. It's powerful and accurate. I'd recommend buying one tuned from Mike Melick. Go ahead and cough up the extra $$ to have him use Maccari parts. They're SO worth it.
You can do a search for my thread titled "Chrony results of a few of my toys" over in the airgun gate.