The MS-1 is great bang for the buck. Rumor has it that it shares drivers with the Grado SR125, which is $50 more expensive. Considering that most people think the SR60 and SR80 are good deals at $80 and $100 respectively, getting a better binned driver for the same price shipped worldwide is a no-brainer.
The MS Pro is up against much stiffer competition in it's price bracket. You've got headphones like the HE-500 and D7000 that cost the same and have better build quality and a wider genre bandwidth.
I've only heard the MS Pro for a few minutes, but I do borrow a friend's RS1 on occasion and I do think it has respectable SQ for the price. It's got a highly detailed sound with fast transients that is well suited for rock. Bass slam and instrument separation are OK, but bettered by the Hifiman. Unfortunately, listener fatigue also sets in quickly for me due to the treble tilt and supra-aural fit.