Combine ZP is free, but you get what you pay for!
It will work with smaller files, but has a nasty habit of putting a mirror images all round the outside of the stacked image. Yes you can start cropping, but why should you have to?
I've used both Zerene and Combine programmes and they have never given fringe images. The output image is full size so no obvious cropping has taken place. I'm not sure how they do it, but as both programmes have to be paid for I asume that they work "a bit harder" to solve the problem.You always get a fringe around images that are focus stacked... it's caused by lens "breathing", not the software.