I just put my ancient KS i950 back into use. It’s had one full service after it went a bit saggy, and a couple of DIY ones over the last 5 or maybe 6 years, still going strong. Meanwhile my Reverb that I bought last April is just back from its first warranty replacement. Annoyingly, for something that did not need a whole new post, I could have DIY fixed it, I just didn’t want to invalidate the warranty!
Side note; I’m not blown away with reverb reliability, both of mine have played up in more or less the same way. But people seem to find seatposts scary; servicing a reverb is no harder than a fork and Rockshox have a great service video online. For my model you just need one special tool (which you could probably bodge, but it’s a fiver, so I got the tool), and an oil tool which you can make yourself for about a quid. Don’t be scared!
I don’t know if modern KSs are still as good but the old ones were reliable, and pretty simple too. You can’t really home service the pneumatic part but the rest is easy enough.
I think I remember Thomson feeling that their post was realistically not user-serviceable, but that was part of the trade off for a very long recommended service interval. cancelled out by the fact that you’ll have a warranty replacement before the service is due anyway