They're quite heavy but that's not an issue for me. Best bang for the buck I ever spent.
Bought it around 2015 in used condition for around 250EUR, then upgraded CPU, RAM, batteries (2x as of now), got a bigger SSD and HDD (512GB+4TB) and got an IPS display and a touchpad of the T480 which fits in there.
I just love that laptop. Superb linux support once you figured out how to setup the synaptics driver configs with synclient.
Oh and it's also the last generation (afaik) that can run coreboot as a BIOS.
Overall I probably spent around 800EUR on it, but considering its lifetime (sold in 2013-today) I say it's definitely worth it. So many "Ultrabooks" and Macbook Pros died on me before, because I always overstressed their GPUs.
There's a German Thinkpad wiki that contains all kinds of quirks and potential problems you can get, it's an amazing resource.
The tldr is you should update the BIOS first and update the firmware of your dockingstation with windows running, and then install linux to be safe. [1]
[1] https://thinkwiki.de/ThinkPad-Modelle
edit: Oh and I used an external m.2 adapter to PCI-e occasionally when I have to do ML related work when I'm not at home on my tower. It kinda works but performance is limited to somewhat PCI-e 4x speed even when it says 8x mode is being used.