You have to be a member of the Yahoo group before you can sign up for TM5.......
I'm a member of both groups (and am a territory custodian) and just saw a notice that sign-ups for TM5 are not available for the foreseeable future until both ATCS and TM5 get the Yahoo Groups issue out of the way. I suspect similar may be coming from ATCSMon pretty soon as well.
TM5 has very limited coverage compared to ATCSMon; it requires all new layouts be built which is very time consuming, so there are only a handful. Also, if your goal is to see what's happening on CSX lines, forget it; CSX has converted nearly their entire system to encrypted satellite links and it cannot be monitored. Those few lines which haven't yet been converted are in the process now.
Also, if there are no servers in your area of interest, there is no coverage. Installing a server requires a good outdoor antenna in the right location, in addition to a decent receiver and the computer to handle and forward the data. Costs some money and it's an all-volunteer effort.
As far as ATCSMon goes, you really need to have some computer savvy to get it working, especially with Windows 10. It is
not intended for the general public and never was but rather as an engineer's interesting hobby; getting publicized in
Trains magazine and other publications brought it into the public eye and many people who expect "install and play" software with extensive tech support have jumped on the bandwagon expecting it to just work. As a result there are always "help me install this I don't know what I'm doing" messages on the group.
A lot of people get ATCSMon expecting something like "FlightAware" but it's not the same at all. There are no public web pages showing rail traffic, no really easy way to create one, and the railroads are pretty touchy about that sort of thing anyway.