Your logbook, your choice.
I keep separate logbooks.
That's partly simply personal preference and partly because it gives me room to use separate columns for each helicopter type which makes keeping running totals easier.
If you do go on to obtain a PPL(H), you'll need to keep totals of each type - unlike f/w, you need a rating for each type you add to your licence and will need to keep a record of hours in each. NB: Each type, not simply piston or turbine.
If you're definitely not going to obtain a PPL(H), it's not worth having two logbooks for the sake of a few hours p/ut. But, be warned - the helicopter bug is well-known for getting into your bloodstream. I started off intending to do only a few hours for experience/fun but, once the bug bit .................
FL