Could always colour code them. But I agree the mantis look isn't ideal.
If you know a decent body shop and I mean decent id fibre glass the back and smooth over. You can fit mesh to help strengthen the back. Any cracking could be resolve when painting. Making sure they take it back enough. If it's the plastic may need added support on the back. Really depends on what type of crack and the root cause.
it would be easy for a mid range filler to crack if they didn't do a very good job.
If you're unsure get a new bumper. Most oem ones look dog rough for the money. Id get one from grams and make it fit nice. Wouldn't sell the oem one. A little investment in making a fibreglass bumper be well worth it.