What is the experience/wisdom about this die? Does it eliminate the need to trim for length? How?

I don't have one so I'm speaking from "hearsay" on the chatrooms. I guess it does a better job than normal dies. I think the secret is it doesn't use an expander ball like other dies.
You do have to do a good trim before using the die so you are hitting the "ground running" with the right case dimensions.
All that being said I think money is better spent on a stoney point (now hornady) headspace bushing kit. Set your dies up so you are barely pushing the shoulder back for ea resizing and I'll bet you'll reduce trimming alot. Bottom line is spending $40 on this kit and you'll trim less with ALL YOUR DIES or spend $25 on one caliber of the x-die and you'll probably see there is a big value difference. I also have the inserts from sinclair that let you measure ea rifles chamber to see what the REAL TRIM dimension should be. Most my rifles are at least .010 to .020 longer than saami. Bottom line is I NEVER have to trim for alot of my guns with normal dies.

PS--the talk about the x-die has pretty much died off.....I don't think it was much of a ground breaking invention.

I was cleaing out a cabinet and found I had bought a 300 RUM that I foregot about. I justed started using it and have loaded 6 times and the brass has not grown much and and I have not trimmed the brass yet. So I guess they work.

Here's an explanation I posted some time back. X-Dies do prevent case stretching in the FL sizing process. If you want I can post the much more in depth test I did using an X-die (.308 Winchester) with cases fired in a GI barrel on an M1A.

While some case stretching can occur to cases in the chamber most often the damaging type of case stretching happens in the full length die. The amount of case stretch you will get with normal FL dies is effect mostly by; the case body taper dimension (particularly circumference), the difference between the chamber and what the FL dies size the cases back to, and the intensity of the load. When the cartridge is fired the case expands (obturates) to the size of the chamber. When the pressure drops off the case springs back a small amount. However, the case does not return to it's original size, it remains larger. Note that your fired cases all are larger in diameter, particularly just in front of the web of the case (expansion ring) and all along the body taper. When we FL resize we squeeze this expanded portion of the case back down close to it's original diameter. When the case is pressed into the FL die this expansion and the body diameter is pushed (sized) back down the brass has to go some where. Since the body taper is most often (especially with minimal body tapered cases) squeezed down before the shoulder area is in contact with the die the brass flows forward. This actually will set the shoulder slightly forward. Thus when we try to neck size only with a full length die many times the case is hard to chamber if it will chamber at all. When we size 1/2 or more of the neck of a minimal taper cartridge (7.62 NATO is pretty close to one) in a regular FL die we most often just squeeze the case sides in. At the same time, the shoulder moves forward and we have difficulty chambering the cartridge. But this discussion is about full length sizing anyway, so now the sides are squeezed in the shoulder has moved forward and the neck is sized. To make the case headspace correct we then complete the FL sizing. The shoulder of the case now is pushed back but the brass is not compressed back; it will flow toward the path of least resistance i.e. forward into the neck. This makes the neck longer which in essence makes the AOL of the case longer and we have case stretch. As you fire a case and full length size each time the brass flows forward and the area in the expansion ring gets progressively thinner and eventually separates. The X-Die prevents probably 80-90% of this by not giving the case brass much room to flow forward as do regular FL dies. The brass still flows forward but to a much more limited degree and the case brass appears to thicken up in the shoulder and lower neck areas. Eventually you will still get incipient case head separation from FL sizing after each firing. But at a much lower rate, thus the number of times the case may be fired is many times more, particularly in the case of an M1A/M14 or AR15. The X-dies also increase case life loading the cases for use in two or more rifles. They also work very well in cartridges such as the 30-30 where FL sizing is always recommended. Additionally, trimming is no longer required. I am not saying that the X-Die is the panacea here as they do not replace proper neck sizing or match loading techniques. For example, with each loading of my 600 to 1000 yard M1A loads I FL size in the X-Die, then outside neck turn for continual neck uniformity (a smidgen is always removed from around the base of the neck). I then neck size in a Bonanza bench rest NS die. This produces very concentric long range ammo with the 175 gr MK seated long. Runout is always under .004" with 90% of the rounds being .000 to .002" runout. That is very good for FL sized ammo in cases that have been fired multiple times!

Larry Gibson