Just to kick things off: if you’re in the USA that booster is quite illegal, likely for multiple reasons. There’s a cap on transmit power on 2.4ghz at around 150mW. And anything that transmits needs s licence.
Beyond that, the metal case is to prevent the RF noise the booster makes from escaping Anna’s playing merry hell with devices of all sorts within a few hundred to thousand meters.
Exactly what devices will be effected in what way is hard to say. The fact that it has such a gnarly case implies that it’s RF noise radiation is a mess.
This is with the case that it’s a FCC violation or three btw. (Unless, to my surprise, it has a legit FCC section 15 sticker/stamp on it)
Without the case:
Your can expect worse WiFi for everybody within X meters for starters(where X is 10-500), and I don’t think I’d use it around anybody who has an older pacemaker or other sensitive device.
Your sticks may have random inputs from the RF noise, your TX may randomly crash/reboot, etc.
Or it may work perfectly with and without the case.
Just don’t disrupt an amateur radio person’s WiFi as they have the means to track you down and turn you over to the FCC, and the fines are huge.