We looked at several other firewalls with supposed WAF functionality in them, but they all wanted you to write your own Microsoft/Metaswitch rules. 

We evaluated a few beforehand, however Loadbalancer.org was the one which was recommended to us by our software providers. They just told us it was the best one for us, so that's why we chose it.

We evaluated KEMP, F5, and Windows Integrated Load Balancer.

We proceeded a long way down the road with F5, then decided to go a different direction shortly before the production environment was built.

We had load balancers from before, that were just kicking around, so we used the ones that we had before, and they weren't a very good match. Then the supplier said, "Use these instead," and that's what we did. They were afforded somehow, (I have no idea how that money was found, or how much they cost or anything like that). But we switched over to what they said and haven't looked back.

KEMP LoadMaster.

We evaluated a couple of others and then decided to go with Loadbalancer. We evaluated KEMP, Zen, and F5.

To be honest, our filtering partners said that they had done that work previously themselves, they had tried and tested, and they recommended Loadbalancer.org. So we just went with their recommendation. We, ourselves, didn't evaluate anything else, but I know that they have. They'd be in a much better place than us to do those evaluations.

We also looked at Kemp. Before this, we were using an in-house version of HAProxy, but ended up needing support.

I do not know if my company evaluated other solutions.