First off, I've got to say I don't see muzzle threading as anything but a PLUS--different perception.
Purchasing a suppressor follows this general path: selection(either doing the internet research or visiting a NFA dealer), application(filling out the paperwork, getting fingerprinted, paying the fee), waiting the interminable time for the application to be processed, and picking up the item at the dealer chosen to accept/conduct the transfer. The last wait time I suffered was less than 6 months vs an earlier one that took 13 months.
A first time NFA buyer has some options as far as the "ownership" issue. If purchased by an individual, the NFA item is in jeopardy if that person dies or becomes legally unable to own the item. Using a trust protects the asset and also has some storage advantages.
We use Silencer Shop for our transfers. You can find your local(?) dealer through their website. That greatly simplifies the buying, stamping, and delivery process IMHO.
Choices?? Lots of choices BUT availability is every bit as variable as any other gun/ammo type equipment at this time. Again, Silencer Shop has a large selection and tells you right up front which are in stock, on backorder subject to delivery delays, or just out of stock. Some local dealers keep display models on hand for a buyer to see first hand. Some dealers may charge a secondary transfer fee unrelated to the $200 NFA tax stamp.
Prices?? Prices for a 9mm "pistol" suppressor can range from $299 (Witt Machine Naughty 9) to some models close to $1K. The difference comes from name brand status/reputation, build material, and effective Db reduction.
Another factor is the capability of some "pistol caliber" suppressors to be used on rifles firing rifle caliber rounds. I have a 9mm from Torrent Mfg that is said to be capable of use on a 300 Win mag with 20+" barrel.
Here's what I found when I was developing my AR9 PDW over the past year: A carbine will handle a heavier suppressor and the weight isn't as noticeable as it would be on a handgun. I also found it difficult to find ammo that remained sub-sonic in a barrel over 5-6" long. My 10.5" barrel pushed even the 147 grain ammo labelled "sub-sonic" over the threshold resulting in a supersonic bullet signature. Only dedicated handloaded ammo stays sub-sonic from my 10.5" barrel although I did find some 150 grain ammo that had only around 25% that exceeded the speed of sound. A suppressor won't make your new carbine "movie quiet" but it has it's niche applications.