Yes they are very convenient, but generally not as stiff as road shoes - and stiffness is the key.
But regardless, I simply don't know how people ride on typical vestigial SPD pedals without a bit of foot support.
You need this sort of thing
[
Shimano M424 image from Wiggle]
Yes they look awful and uncool but they do the job very well. I hate how they look but I've used them these last 12 years or so.
If you use MTB-type shoes with treaded soles and recessed cleats you may well need to hack some sole rubber away to make these safe - that's what I do - otherwise you can easily find your feet totally locked in, be warned.
If you use road shoes, then get decent ones with carbon-reinfoced soles - totally rigid, very nice. LIDL - er no.
But you still have the issue of an unsupported shoe, there can be a outward swivel of the foot (reverse pronation??) which is simply solved by using pedals like the above monstrosity.