Hi,
The -k8 is just the ASA 5510 with a base license, while -BUN-k9 is sold along with a security plus license.
They are named according to the package they are sold in.
You may also find ones with AIP or SSL in their names, which means they were sold with an AIP-SSM or SSL licenses respectively.
The -k8 does support ISP failover, as there is no special license required for "sla monitor" commands.
Hope this helps.
