Looking at linear comps for a 458 socom carbine/ rifle build - have a barrel already, going to go with a Tromix bolt (keep waiting for them to go on sale, don't think its going to happen), and wondering about a linear compensator for the build.

Kaw Valley offers a 2.25" and a 3.5" - any real difference in performance anyone knows of?

Other options folks have used?

I've only ever used the one Tromix sells but have been very happy with it

ETA mines a radial not a linear

@TonyRumore

I've never seen a Kaw unit first hand, but it would appear the main difference is the Tromix 2-piece design versus the monolithic design of the Kaw.....which of course makes the Kaw cheaper to produce.
However, I imagine the functionality is about the same.

The Tromix 2-piece design allows us to stock the rear ends in various thread pitches and the front ends in various exit holes, that way we can mix and match the two in order to get whatever thread pitch and caliber combination the customer might need.  We can assemble about 900 different combinations considering we also have black, stainless, and two-tone.  For example, we can quickly assemble a 3/4-24 22 caliber device for a big bull barrel if need be.  

Tony Rumore
Tromix

I've run the standard sized KVP on several things, including a 450BM.
Makes a noticeable difference in blast.

Two piece Tromix Linear Comp for the win.  That is what I use on my .458 SOCOM and it get's it done.  I had a KAK linear and it was a piece of crap.  I am very impressed with everything that Tromix makes.  Also the Tromix follower for the Lancer L5 mags are a must in my opinion.

I have used four blast diverts, or linear comps if you wish.  The TROMIX, Midwest Industries Flash Can, Noveske KX3 and KX5.
The most expensive by a long shot are the two Noveske items, the KX3 and KX5, roughly $128.  On top of their higher initial cost, you have to pay to have someone take them apart and open up the blast cone.  The old ones were easily disassembled but not anymore.  The last one I bought will not come apart no matter what I have done and short of taking a hammer and blow torch to it, I've tried it.  So, currently, I fail to see how it can easily be opened up anymore so those two, as far as I am concerned, are out of the question for using on anything over .30 caliber.  On one of my first KX3 used on a 7.5 inch 5.56, after a thousand rounds or so, there is considerable flame etching on the cone.  I have not seen any etching on the cones of the ones modified for .458 SOCOM.  Also, when used on a firearm shooting cast bullets, it needs to be taken apart after every outing or 50-100 rounds and thoroughly cleaned of lead deposits or it will solder itself shut.  The new ones, since you cannot take them apart, IMO, should never be used with cast bullets.  I can see lead building up in them over time and causing a problem.  It is also a heavy unit, and IMO it's this added weight that causes any recoil reduction but it does a very good job of directing blast down range.  Installation is not as easy as the TROMIX or MI because it will need indexing if you are like most people, wanting the Flaming Pig on the side, right side up.  The KX5 wighs 4.5 ounces, the KX3 7 ounces.  

Next is the TROMIX.  It looks great, comes apart easily, and does not need any modification.  At $95, it's worth every penny.  I have not seen any flame etching on the interior of the unit but it needs to be taken apart and cleaned fairly often if you are shooting a lot of cast bullets.  The lead vapor deposits can build up and almost solder it together, just like the KX3 and KX5.  As with the Noveske offerings, it does an excellent job of diverting blast down range and it does offer some recoil reduction, but I believe it also does this because of its weight, because being made of steel, it is a heavy rascal, 8.0 ounces.  All of them are quite heavy and that can be a pro or a con, depending on its users desires.  The unit does not need indexing since it is symmetrical all the way around.

Cheapest is the MI.  It is an aluminum one piece like the KAK and does not ever need to be taken apart to clean and the .30 caliber flash can has an opening more than big enough to pass the .458, so no modifications are needed.  Just screw it on.  It also does not need indexing.  I have it on several calibers from 5.56 to .458 SOCOM and I see no flame etching on it at all.  It does an excellent job of directing blast downrange but it weighs next to nothing (3.2 ounces), so don't expect any recoil reduction.

Last comment, the KX5, TROMIX, and MI units will all fit under a skinny handguard, like the MI Combat or other skinny handguards.  The KX3 will not fit under the skinny handguards, and if it does somehow fit under it, it will be so close as to in danger of making contact during barrel flex.  For it, the handguard needs to be more generously sized, like the MI Suppressor friendly handguard.