Depends on your own personal discipline 😉
As long as you are able to monitor both simultaneously if you should need to (eg at moments when everything is jumping around). And as long as you don’t lose track of your total exposure when holding the same stock in both.
Also, spread betting firms place a limit per person on some stocks on some occasions (eg, IG won’t allow most of us more than £500pp on TAN at present), or have different exposure levels themselves so that one firm might be accepting online bets at a moment when another isn’t.
And bearing in mind that spreadbetting means holding leveraged positions, take an even greater degree of care as when limiting your number of credit cards.
Also don’t make the mistake of fully utilising one account before employing the other. (leave sufficient headroom unused, to accommodate variable margin requirements).