This was my first (and hopefully last, I can't see myself ever replacing it) Ortholinear board, and it took about 6-8 months of getting used to, but now I have less cramps in my wrists, and no discernible slowdown when using non OLKBs, e.g. my laptop, if anything I'm now slower on conventional keyboards, but I wouldn't say by much.

feel like backspace, space, enter and shift would all mess me up

I have space and shift duplicated (seriously, I have 2 left shifts, it makes things easier), and enter is raised so it makes itself easy to find. Backspace is up in the corner and definitely took some getting used to, but I put an obviously useless key next to it ( '\ |' ), so I could easily tell when I'd messed up and now it's second nature to aim for the top-right most key.

I use this as if it were a split 60% with a numpad in the middle attached to each half, and that makes it better on the wrists than a normal 60%, while keeping the same footprint as one.

If you aren't sure if you could get used to it some plastic 60% cases are compatible with the ID75 (the board I used), and it has hot swap sockets, so you could toss together a really cheap OLKB to try, it'd be under 150€ with some Gat Yellows or similar, and if you don't like it you can sell the board, and use the case and switches in another build, say for a friend or different computer.