what is the F5 equivalent of a Cisco ace20-mod-k9

We don't really have anything that low scale, except maybe the VE or 2000 Series, but it really depends on what you want to accomplish and any security requirements you might need to meet.

One important note is that the F5 BIG-IP is much more than a simple load balancer and can help you replace / consolidate quite a few point solutions and at the same time enhance your security posture.

You can find specific product specification in our platform data sheet: https://www.f5.com/pdf/products/big-ip-platforms-datasheet.pdf