I have the 1st gen X1E. It is a great laptop but it does have two major flaws. 1) The battery life is very mediocre, especially so on the 4k. Mine gets at most 6-7 hours and this is undervolted. 2) The display is a bit of a crapshoot. Mine (4k) has issues with grey banding and backlight bleed. Tried getting it fixed but the replacement didn't make much difference. Its not a deal breaker and I have another year of warranty left, so plan to try again in the future. The 2nd gen still have mediocre battery life, no idea about the screen.
I got an excellent deal on my X1E. If I had to buy it at regular price, I probably would have paid more for the 16 MBP.