Hello and welcome!
Gmail uses https and it works fine, so I believe your web page would work as well.
Yes, it is a bit slow to open web pages, especially if you are used to broadband but you must understand that Boox is not a device that has browsing as it's primary function. It is firstly an ereader, WiFi is just an extra.
All I can say is that I'm very satisfied with mine and I don't plan on getting rid of it any time soon.