Yes, it is very tough. Truthfully, you will never break it. Since the other Strider fixed blades are made from .25 inch stock, the MFS is not going to be as strong as these. However, that doesn't mean the knife is wimpy...far from it actually. It is very stout. Listen, Strider will not let a wimpy knife out of their shop. They have the reputation they have for a reason. All of their knives perform well and won't fail, including the MFS. Hell, the MFS is thicker than most other knives of its size anyway. Bottom line, use it, beat the hell out of it, it won't care.
Neck knife? Not for me, too heavy. Plus, I am not a big fan of neck knives anymore.
No, sheath cannot be used IWB. It uses a Tek-Loc. However, I am sure that one of the custom sheath makers on this site can help you with that.
Is it worth $175? Definatly. Actually, it is worth far more. I think it should be priced around $225.