As safe as you can get with a backported browser. The OS is the real problem, I wish updates could also be backported.
Lol. That has been the topic for several comments. Banks reacting negatively to version 115esr. Now being completely blocked. SOoooo, if the bank thinks you are using Win11 with a modern browser then you have full access again. If we continue to use Win7 years after all updates have stopped this is the only way it works. Something we use spoofs our actual OS & browser into something current the websites are tricked into giving us service. For it to work there must be a general consensus to trust those providing us with these modified browser versions. The ones being mentioned are being used by a large number of Win7 users without complaints. It is here in these forums where we find safety in those reports. IMHO Supermium is doing the job we require allowing us to exist in a more modern world with our outdated OS.
The problem is that Useragent spoofing does only help against Useragent scanning. There are other ways to check the browser and OS (like over JS, which banks require you to activate), might not be so easy to counter all of the possible checks.