I have the 42mm GSO SV (see review section) and don't find it crap.(what are they smoking)
I use it in my f6 Newt and my f7.5 refractor and find it 's performance great.
It is not a TV or other super high priced EP , but it is certainly not crap.
Yes exit pupil size in an f5 will be a determining factor although I have tried it in an f5 GSO Dob and it was still OK for me at least.
Didn't see the Central obstruction , only on the moon , but obviously it will be coming into play at f5 .
The 30mmm would be a better proposition for the f5 Dobs .
I don't have a 30mm GSO SV but have used one and the quality between the 42 and 30 was the same in both of my scopes.
May be there crap because they weren't selling and every one went to the opposition for a cheaper price?
Mark