there is a huge difference. huge.
PAR2
checking is hardly CPU intensive.
Checking is mostly limited to what average speed your HDD can pull.
I'm also not so sure Repairing something is that much cpu intensive either, it appears to me that it's also relative to HDD speed (faster repairing on my RAID machine than on my single drive machine).
Where a multi-threaded oriented build of par2 would show huge benefit is par2 block creation, which is very CPU intensive.
Take your pick:
There's not enough incentive at this time to implement a new multi thread build of par2 in Alt.Binz cause Alt.Binz doesn't make pars, it only checks & repairs.
-or-
It's a fresh build with a few major changes on it, give it a few weeks/months before it becomes stable and has bugs ironed out before considering using it embedded in something like alt.binz.