I have used the 13900hx/4090 variant for over a year, and I must say I was impressed. They are very comparable in every aspect, you can even use xmg bios in their machines (it does not void your warranty to do so), they're that similar. Although they are not the same, i.e. they do not have advanced optimus and the memory/ssd options are subpar. To my surprise, they also have quite good after-sales support, as I was able to replace my machine due to a small issue even after a year of purchase, and they made it quite easy to do so.
Considering the price difference, pcspecialist is the better option imo.
