I worked with BigIP for a few years, and I believe that the real value is in the support contracts, and the peace of mind that gives to enterprise execs. failover (local or global) as well as state sync is all do-able with linux or bsd, but that will take time and work. BigIP is more or less plug and play. This is the case for many "enterprisey" products. Personally, I prefer to go the linux/bsd route, since it forces you and your team to have a deeper understanding of what you are building, which is really handy for when things break.