Don't just bondo the crack. Fusor products work really well for repairing damage to polyurethane. You'll have to repair it from the backside for it to hold up. If you just repair the front side it's going to look nice for a while but not hold up in the long run. Some people will try to plastic weld polyurethane back together, and while you can plastic weld it, that particular plastic is very hard to weld properly and it's just easier, faster, and better to use a product like Fusor. Though for all the products the repair method will be similar the exact way you'll repair it will differ slightly based on the product you use. Usually for most things I stick with Fusor 100EZ and 114, and I do use the Extreme Plastic Repair in some situations. SEMS, Duramix, 3m, etc, are also other companies that have products like Fusor, but I personally use Fusor, however Im sure the other companies products are of similar quality
If I was you I would save a few bucks and take it to a shop and have them fix it and paint. Given the crack isn't huge and a new bumper doesn't cost that much to cancel out the repair work.