It's been awhile since I've had to use one so I'll defer to more current-owner responses but IIRC they're just sized to the trailer. The weights determine the size/stiffness of the "spring bars" in the kit and you want the closest size to your trailer's "wet" weight rounding up (if you've never weighed yours loaded, just take the dry and add 10% or so). So for a 9,300lb trailer you'd want a 10,000lb kit. Don't go higher than you need or you'll get too stiff of a ride.
There are at least 3 styles of these. I don't know their formal names, but we had the kind where you install the bar in the hitch and there's a chain you attach on the trailer side to a cam-over bracket on each side. You can make small adjustments in the ride by choosing which chain link to connect to the bracket but I always found the system a little fussy. You may want to watch some Youtube review videos to decide which system is best for you.
Our system came with an anti-sway device as an optional add-on. I highly recommend it. It made a VERY noticeable difference reducing sway. You just have to remember if you're going in or out of a steep or angled site to take it off because it can get bent - it doesn't have a ton of range of motion. But it's not normally under pressure/tension so this is just removing a pin and popping it off. These devices are just simple linear brakes - a steel bar inside a friction-material sleeve. They can squeak if they get get or any kind of dirt inside (which they will) but they're still worth it IMO.