I have used only cheap knives so far -- and 2 out of 3 have been very good. The problem is the sheaths rather than the knives. A good quality, well designed, low profile sheath might be a better bet than custom knives.
That said, I have now learnt several tricks to help avoid loosing knives (I lost one -- really nice design & construction & cheap) and might get something a little better next time. I can't ever see spending more than 20 pounds ($36) on even a very good dive knife -- and I usually spend less than half that. However, the Riffe (speargun) clientelle must be "well minted" (US doctors & dentists?) -- I reckon they would happily pay 2x or 3x what I would, if the design & quality was right -and a customer service would presumably offer to make the clients design. Spearfishermen after the real big fish -- probably look on a very good knife as an essential tool rather than a luxury. Spearo knives tend to be pointed, stillettos are a good design -- like an old British WWII command knife, but flatter with one serrated blade & one plain. There are only a few good ones about, the Sporasub Snake dagger (with zinc pommel to resist corrosion) is about the right size & shape, several companies make ones which seem good but a bit small to me (OMER, Rob Allen, Riffe, Imersion):
http://www.bluewaterhunter.com/shopsite_sc/store/html/shop_knives.html
I don't think a line cutting notch is necessary or desirable on a thin blade like this -- a strong, sharp edge and a serrated back & no-loss low profile sheath should be enough. I like a biggish blade as I clean my fish with my dive knife -- boat-based spearos after big fish may carry separate tools (including saws!), so you might want to talk to them about their needs. BTW I have heard some spearo's hammer their fish with the pommel to finish them off (unusual though). Spearo's also sometimes carry an ice-pick type tool, for a quick, clean coupe de grace -- instead of a stilletto (although a dive knife would probably still be a good idea). There are some cheap home-made designs to be found on the internet forums -- but a few comapnies sell good ones - Rob Allen among then.
If he can make me something like a Sporasub Snake, with a serrated back & decent flat sheath for under 20 pounds -- contact me!
