hi graham,
I have only used a friend's one for visual - and that was some time ago. they are of course good, I'm not sure if I'd say they are
way better than the MPCC.
They are designed to go down to F3 I think while the mpcc is f3.5 and up. The have a 2xdoublet lens design and I think the mpcc is a triplet.
at f4 I'm not sure it's worth the extra $ for having the same BF and not using a scope closer to the f/3ish limitations.
there are other options out there too worth looking into if you were certain on changing from the MPCC such as:
http://www.teleskop-express.de/shop/...pe-ab-f-4.html
http://www.teleskop-express.de/shop/...-175-fach.html
Or the baader Rowe. the MPCC is a great little performer for the price as you know but I think when using at f4, personally I would put the $ into a focuser or OAG (although then you might need one with more BF).
Don't let me dissuade you though, others may think it is well worth the money.
Best of luck
Russ