Below are my thoughts based on my personal experience with split space bars.
Keyboards I've used with split spacebar:
- Tina variant C (real HHKB, i.e., 6u spacebar version)
- 0.01 Z70 keyboard
- KBD Maja (Alice "clone")
The most important thing:
Know the exact position where your fingers press the spacebar!!
Know the exact position where your fingers press the spacebar!!
Know the exact position where your fingers press the spacebar!!
Repeated three times for highlight.
When you have decided on the splits for your spacebar, make sure that you fingers press somewhere in the middle of the spacebar keys. Otherwise it'll be very uncomfortable, because you either often miss clicked due to your fingers naturally lies between two keycaps or you have to readjust where your fingers are to press the space bar.
Now when you have chosen a split spacebar location that does not interfere with your natural way of pressing the space key. The worst scenario of the split spacebar issue is you are not using the splits. While you gain no benefits from it, it also dose no harm to your existing way of using keyboards. It might feel a bit different than using the large spacebar, but from my personal experience, it doesn't really matter that much.
Now for the utility point of having split spacebars (again, based on my personal experience):
When I'm tying, I exclusively use my right thumb to press the spacebar. And my pressing location is somewhere under the "B" and "N" key on an ANSI keyboard. However, when gaming, I have to use the left hand for pressing the spacebar in games (as many games needs to use the spacebar).
Now here is the issue, if I want a split spacebar layout, I need to have two spaces anyway for both my left and right hand when gaming and typing. So the split essentially does nothing besides adding an additional key between the spacebars for FN use. Meanwhile, as a HHKB user, I've already have the habit of using 1.75u right shift + FN or the bottom right key as FN. So essentially, the split spacebar layout gives me no improvement over existing layouts.
However, after time, I've discovered a great usecase for split spacebars. Having spaceFN on the right spacebar. Previously, I've used spaceFN and really liked it, but because how spaceFN works it conflicts with gaming, so I had to move away from it. Now with split spacebar and with me exclusively using the right hand for space, I can set the right space to be spaceFN and left space untouched (i.e., normal space). Which worked super nicely.
Personally, I didn't stick with this usecase, because I switch keyboards like every other day and prefer to have a uniform layout on every keyboard so switching between them will be agnostic.
Hope my input based on personal experience helps with your decision.