Sal, I think the SWICKs are a little too much knife. Part of my thinking with wanting H1 is a knife that will ALWAYS be on the user. I can have a model to you before end of February, if you want to see it. I do agree with your caution with a neck knife~ goal is ultra light, here.
Edited to add:
FB14P is a lot closer, weight-wise, than P2.
Just a ouple more thoughts. I have a few neckers and IMHO weight and size are both important factors in whether the knife will be carried. The Swick is 1.4 oz. and a kydex neck sheath would not add much weight. You get a 2 1/8" blade, and I don't think you'd want to go much shorter than that. Overall length is approximately 5 1/2". Now let's compare a couple of other knives.
1. Swick - 2.125" blade, OAL 5.563", 1.4 oz.
2. A.G. Russell Hunter Scalpel - 2.25" blade, OAL 4.75", 0.5 oz. It is a very lightweight knife, so it is comfortable to carry, but is so tiny that I would not trust it in the situation you describe. For me, I can only get two fingers on the tiny handle.
3. A.G. Russell Woodswalker - 2 3/8" blade, OAL 6 1/8", 1.2 oz. Fairly lightweight. Handle is a 3 1/2 finger grip for me, but is skinnier than I would prefer to the situation described. For shower self-defense, I say something shorter overall with, say, a three-finger grip and a handle designed for good retention when wet would be good.
4. Old-style Benchmade Tether - 2" blade, OAL 5 5/8", traction coated skeletonized handle, weight unknown. For me this is a great necker. The blade is long enough, the knife is light enough for sustained carry, and the coating on the handle makes retention good, although as Sal mentioned, a hole you could stick your finger through would be even better. The current Tether, which Benchmade sells under the Harley Davidson label, look to be almost exactly the same size, but has some design changes. The old design had a thumb ramp with some jimping and does a great job of keeping the knife in the same position The weight on the new design is listed at 1.6 oz. For me that with the finger hole would be pretty close to ideal, and it is coincidentally the same length as the Swick. Any shorter than that would be too hard for me to keep ahold of.
5. ESEE Izula - 2.75" blade, OAL 6.25", 2.00 oz. It's the biggest necker I like to wear, but I think it is bigger than you need and you would want a different sheath.
6. Becker BK-11 - 3.25" blade, OAL 6.88", 2.50 oz. I had one and sold it because it was too large and a bit too heavy for me to wear comfortably for extended periods of time.
7. Orion K2 Backpacker - 3" blade, OAL 6 7/8", weight unknown, but IIRC it's slightly lighter than the BK-11. It's a nice knife, but I think it is too big and too heavy for what you have in mind.
8. HAK (Hideaway knife) - I had one a long time ago, but sold it. It would have been a good knife for what you are describing, but there were different size handle openings and you had to measure your index and middle fingers around the knuckles and order the appropriate size. I think for you project a generic handle in a one-size-fits all knife would be a good thing to consider.
Conclusions? First of all, it's your project and your safety, so you and the folks there are the ones who need to be satisfied. However, based on the neck knives I own or have owned, the Swick seems ideal or very close to it. Since you are thinking self-defense, you might want to consider having it done in a full-serrated edge so that sharpness will be less of a concern.
Good luck!
And, yes, a natural swinging motion of the arms is the way to use~ but should also be designed so a stab- because a stab will always happen eventually if the slashes alone don't do it- won't injure the defender. Again, the index finger hole will help make this safer.