But im unsure on what the difference between these are? as I cant seem to find there specs and what they can / cant do..
We have several F5 units old D25's and a pair of the new 6800's. We have had nothing but problems with the new 6800's and the new 9.4.x code. The old 4.x code was much more stable. lacks alot of features but at least its stable.
The nice thing about the new F5's is they are a load balancer, switch and firewall in one, doing nat and snats. They will not support irules if you have a problem unless you want to pay their 250/hr "professional" services fee to have them help you build their irules.
Zeus load balancers are great, we have a few of those as well, they are only a full proxy load balancer, they wont do any snats or nats etc you'll need your own firewall pair to do that. Zeus support team is great, they will help you with trafficscripting, and everything under the sun.
The bigIP d25 and D30's will only support 400Mbps thats it they flatline after that, if your looking to do big bandwidth you will lneed the newer F5 units or something like zeus's ZXTM. If your not serving large media downloads, F5 works great, if you are serving large content please stay away from F5. There is a rather large bug we discovered with F5 relating to their fast http profiles which are not dropping idle connections like they should be, ever see a load balancer keep 400k connections and every 8 seconds send fin acks to each one? yes a fin storm that basicly makes the load balancer kill itself. Restart the TMM engine and 2 seconds later your back in business, but the 1.3Gbps you were previously pushing is now half that because your sessions were alllllllllll reset.
We have not used any other machines such as cyotepoint or barracuda's LB's. Or any netscalers but i'm sure netscalers would work perfectly fine. Don't trust some small name because they are cheap, they are probably just a linux machine running LVS with a few bells and whistles if you need basic load balancing go with LVS. Its cheap, its free and it works.