This is worth specifically addressing to potentially avoid issues in the field.
In general, weapons sold by vendors at the event are not vetted for suitability or weapons-checked for safety.
Any trader should be able to tell you if similar weapons they’ve made have had issues at PD systems before, or if the weapon is wholly unsuitable in some way (e.g., being a gunblade, or a 8’ weapon that’s not stabsafe), but the responsibility is still entirely on the buyer to ensure they’re buying something appropriate and to have it weaponschecked themselves.
Edit:
Right, flails.
The main things to remember are 1) don’t put a core in the flaily bit, 2) foam is weak and tears easily.
The former will have your flail failed faster than you can say ‘flail failed’ without messing it up. This is because you can’t actually directly pull blows with the flail, so you have to have it constructed such that when it hits at speed it just bounces off harmlessly. A good basic mental model for the head is a throwing weapon, as that’s pretty much what it is.
The second will just cause your flail to stop being a flail quite quickly, because as soon as it strikes over a shield or round a parry it will tear apart. To mitigate it, you want to reinforce the links with something. One common method is to use leather or strong linen glued and sewn into each link, and then wrapped in foam before painting. This gives you a flail made out of separately swinging links - although it tends to work just as well to only have a couple of ‘real’ links at the point the haft joins to the chain, and have most of them just be a fake chain made out of foam. The other interesting option is to make the chain entirely out of foam carved to look like a chain, and run paracord or climbing rope or something down the centre of it to hold the whole thing together - if attached sufficiently firmly to the core of the handle, this is then basically impossible to break. Doesn’t work so well with having a nice looking chain, though.
Once you’ve got past both of those, it’s basically a matter of “don’t make the head too heavy”, and don’t make the chain too long. For a 1h flail, a 20" handle works well with a 14-16" chain+head construction, to give you an overall size of about 36". Going up to 42", I’d suggest a 2ft handle and a 18" chain+head. If you decide to do something crazy and make a 2h or pole flail, I’d again suggest a chain not much beyond 2ft at the absolute maximum, it’s just uncontrollable otherwise.
I hope this helps, but I would finally advise that flails are a right bastard to make, and it’s probably significantly less faff to buy one than to make one, especially if you put any sort of financial value on your time.
