Cisco Firepower as AnyConnect VPN concentrator

Hi,

We're going to be demoing a couple of Firepower 2100's solely for the role of AnyConnect VPN concentrators. We have extensive experience using ASA 55xx-X's for basic firewalling duties but are a little put-off by reading all the bad experiences with Firepower so some questions upfront:

• Is Firepower a good fit when used solely for the role of AnyConnect VPN concentrator?
• Is there a good up-to-date overview of any missing AnyConnect features compared to ASA?
• It seems it's also possible to run legacy ASA on the Firepower hardware but we're not certain if this a good choice because we can't seem to find a roadmap for this. Is this a solid choice futurewise? We're aiming for a 5 year lifetime and want to avoid a forced migration to Firepower during this period.