BTW, the site : btckey.space is run by Jude Austin(https://bitcointalksearch.org/user/jude-austin-105076) , its official thread is : https://bitcointalk.org/index.php?topic=1005950.100. If your findings are correct, then post on its thread and lets wait for the owners reply.
You can be sure they do that.... i put 2 keys i had for year just to test them... he seem to be poor and desperate that he took as small amounts as 1600+ and 1200+ satoshis... But i also payed a very small price to see the truth!!!! Now you guys know why they keept source code secret ... never use sites like thoose... build ur own directory.io and use the source... i will help you if anyone need help to setup it.
the only weak thing is the sourcecode allows maximum 208 keys to be checked at same time i cant change it since this seems to be what blockchain allows at runnig cors. if anyone can make it better , would be happy if u tell me to.