The pool advertises itself as an FPPS pool with a 2% fee which is lower than the vast majority of other FPPS/PPS+ pools, which raises a flag - although some people might say this is a marketing thing because they are new.!
The second flag: they claim to have 822PH/s, so that should result in a block every 30 hours or so, but using
blockchair to search for blocks found by GreatPool showed 0 results, assuming there is a spelling problem of some kind I went ahead and manually checked all the names of the mining pools that found a block in the past 5 days up to this last one, and the result again was zero.
I don't have solid evidence that these guys are scammers or anything like that, but I didn't find any reasons to trust them, and with that many more other options (that are actually trusted), I rather not take the chance.