We've been using aspen for years with good results.![]()
We were not changing the whole substrate out very often, just picking up poos and tossing in another handful, and then we got a stinky problem. So we are now changing it out every month, slightly longer or shorter depending on if you can smell anything.
Also we have to be careful not to spill water or put anything back wet after washing as it will make the aspen stinky much more quickly.
We use aspen on all but one of ours (our snow girl is just finishing her regurge protocol and will move back to aspen, but we've had her on newspaper just for ease of spotting more problems)
The snakes seem to love burrowing in it, even our adults. They spend long periods of time bulldozing their litter from one area to another and then burrowing into it (reminds me of kids playing in the leaves in the fall)