Before purchasing, be aware that you shouldn't use Atom Logger with Gmail / Outlook or other big email providers worldwide as they might block the program from connecting to the mailbox and therefore deliver your keylogs.
You can monitor multiple computers with a single Atom Logger instance. All keylogs will be delivered using the same method (so same mailbox or server) but each of them will come with computer identifying information.
Checkout can be completed using BTC or a wide range of other e-currencies.
If you aren't familiar with btcpayserver, here's a screenshot that might be useful if you wanna pay with other coins:
Keyloggers can be used safely if you're going to use them to monitor activities on your own computer. Just keep in mind that using them to spy other people is a breach and might lead you to face legal consequences.
The logger can be configured to block specific applications/processes from running while it is executed. This can be useful if you know that some system processes may break it while you're doing your tests.
Keylogs can be delivered ad your favorite timeframe, starting from a minimum interval of 1 minute. Anyway it's not recommended to set such a low timer, else you'll be bombed by logs.