Is this a legit IMEI checking website for AT&T

Hi I went to link below those morning to check IMEI compatibility with AT&T network and wondering if it's legitimate and safe to use? as i only found it thru google search and not directly on AT&T wireless website. certificates look ok, but

all it said when I entered IMEI is "esim not compatible, we added Sim to cart?" lol and it felt sketch :(

https://m.att.com/shopmobile/wireless/byop/checkIMEI.html