You can set up mini-breaks and a long break and decide whether you want to ignore or continue breaks, etc. PrevRSI is not as feature-rich as Workrave but it has worked well enough for me. PrevRSI also uses less memory than Workrave, something that I like, probably at the cost of not having the better UI and more features that Workrave does.
I’ve been using it for the last couple of weeks and it’s been working just fine. Try it, you might like it too.
PS: Even if you do not suffer from RSI-related problems, it’s a good idea to take adequate breaks to ensure that you do not fall into the RSI trap.