In fact, I feel so strongly against it, that I wrote a blog post on how to find work outside of those marketplace freelance sites that force you to use tracking tools.
You might be interested in reading it at https://nickjanetakis.com/blog/how-to-start-a-successful-fre...
If I had to use this type of software to get a contract, I'd be willing to do it (on a dedicated machine), but the payback would have to be substantial. However, it seems like the gigs that require installing this type of software don't actually pay as well as those that don't.
Basically, it is impossible to ensure you're not leaking information while you have such software installed. There are too many vectors. Unless you literally setup a VM per client and ensure you do not check email on that VM, which I suppose is possible ...
I also hired there and I wasn't looking at my freelancers' screenshots. It's just a platform's rule.