Buying a .45 suppressor for use on a 9mm makes sense, but only if he really plans to also use in on a .45, otherwise you have a suppressor that is a bit larger and heavier than necessary and not quite as effective as it could be.
You should be able to get a threaded barrel direct from SIG, also check Brownell's and Midway.
Octane 45 HD had the advantage of coming apart for cleaning so you can use it for .22lr as well as other pistol calibers.
The odd shape of the Osprey puts some people off, but its very effective and makes it easy to tell if its starting to loosen while shooting (a problem that can end up causing baffle strikes).
The Osprey was my first can and I've been very happy with it, I've used it on 9mm, .40S&W and .45ACP. Not so much with 9mm these days since I got a dedicated 9mm can. Picked up my Octane 45HD on Saturday and hope to try it out tomorrow.
Given the horrendous wait times, starting out with one you can use with multiple calibers makes a lot of sense unless you can afford to buy multiples from the git go.
