Electribes offer great bang for buck value imho, very user-friendly. I never sold my EM-1 (still think has a great liquid tone) and while I haven’t owned an ES, I know lots of people on the Korg forums who were as fanatical about their ES-1’s a few years back as some people get about Elektrons. Of course it’s not going to be as capable as something modern, but assuming it still works and the price is right for it it will probably be good fun.
Is it one of the first generation ES’s with the plastic case, or the newer ones with the metal housing? The knobs on the plastic ones don’t age super well, especially the ones that you use for filter tweaking. Try all the controls out before buying.
Get the current owner to demonstrate sample loading for you. Make sure it goes smoothly from your perspective. IIRC some people had issues with this.