Hi, I have 5x 1080 ti for ETH mining and I can guarantee they're great., but there are a few things you must consider before buying.

1) They get 40+ MH/s as other cards do (RTX 2060 super, 2070, 2070 super), but power consumption is higher. They draw 170W even with good tuning, that is 30-40W higher than other newer cards, so if electricity cost is a problem, be warned

2) 1080 ti price is good and maybe roi (return of investment) is faster, but this is a 2017 model. When you buy 5 years old used cards, failure probability is higher and this can definitely affect the roi

3) We don't know for sure, but ETH mining is likely to end this year and 1080 ti was great for daggerhashimoto algorithm, but probably won't be as good with new profitable coins (ERGO, FLUX, RVN...). I'm not talking about performance, it's more a matter of efficiency (performance vs power consumption)