Malpaso, I've got carried and used the Shorty, the Rivermate and the previous incarnation of the Benchmande that Paul180 posted. Any specific questions feel free to ask.

On our rescue vests (Mustang MIV-20) there is a dedicated knife pocket that the Rivermate works in quite well. I think it is the better of the two Gerbers from a knife point of view but not from a sheath point of view.

The river shorty can be mounted upside down and will NOT have any retentions issues, period. The Rivermate's weakness is in the sheath's retention system. The ones I purchased were retained by two stainless steel pins mounted in tiny o-rings. Any kind of shock loading, if mounted upside down, could release the knife from the sheath. The sheath fits a lash tab well and as long as it's not upside down, it works just fine. I don't know what the newest ones are like, so I'm not sure if there has been a design change.

Both knives are reasonably corrosion resistant. The Shorty is highly polished while the Rivermate is coated. Both will benifit from Tuff cloth or Corrosion X or ACR50.

The previous version of the Benchmade dive knife is far and away my favourite. It has a bullet proof retention and mounting system and will simply not corrode.

I have to ask why the focus on the blunt tip. Our requirement for blunt tips is driven by the fact that really pointy tips and inflatable boats don't mix well. Unless there is a rubber boat in your future or there is a specific requirement re cruising, the blunt tip is limiting. There are lots of newish blade designs like a modified drop point (Gerber's DPSF folder) that are reasonably boat safe but still have most of the advantages of a pointed tip.

The newer Benchmade is a fine knife with a good retention system and a great steel. The notch is good for cutting monofiliment if tangled while diving but isn't meant for cutting lines as such.

This post is already too long but if anyone wants to discuss tow post knives...that's another thread.

Jenks