Head Direct has a 30 day return policy, so you're not exactly trapped to them if you end up not liking the set.
The RE0 is a well done IEM that is a great deal at the $99 price point.
I have not heard the MS1, so I can't comment how they compare to what you prefer. Laokid18 suggests the MS1 leans you more towards the Phonak Audio PFE IEM. The price range is still excellent on this product too and is another outstanding bang for the buck option.
I think the choice would come down to personal preference. I've used both the RE0 and PFE as well as a number of other IEMs. The RE0 didn't match my preference in sound, so I lean more heavily towards the PFE which in my opinion is a little better (very different sounding) product. I would also add one more product up on your list, Denon's C751. This is a really good IEM with a very realistic sound. It has a couple short comings, but they can be overlooked. The Denon C751 simply has great realism that I haven't really heard from any other IEM.
As I said, the end choice will much more be a matter of personal preference. For example all 3 above sound very different from each other, but each offer their own great qualities that excel some way in the market. As well, none of them do anything terribly wrong. Each is a well functioning product that is also decently special in their own little ways. I've done mini reviews of everything I've run if you want to get a more specific interpretation of my thoughts:http://www.head-fi.org/forums/f103/m...4s-ok1-369643/
A good number of headphone reviews exist for these:
RE0techPowerUp :: Head-Direct RE0 Earphones Review :: Page 1 / 4Head-Direct RE0 ReviewAmazon.com: Customer Reviews: HEAD-DIRECT RE0 In-ear Headphones
PFEPhonak AudÃ©o PFE (Perfect Fit Earphone) ReviewAudeo PFE 122 Perfect Fit Earphones (black) Headphone reviews - CNET ReviewsAmazon.com: Audeo Perfect Fit Earphones - Black: Electronics
C700/C751Denon AH-C700 In-Ear Headphones (black) Headphone reviews - CNET ReviewsDenon AH-C700 review from TechRadar UK's expert reviews of HeadphonesAmazon.com: Denon AHC751K In-ear Headphones (Black): Electronics
...you get the idea, and I'm not even including the 50 threads covering these things here on Head-Fi to boot.