Peplink with existing VPN connections

I am currently looking at the peplink balance products to replace our current site to site VPN connections and add WAN aggregation at our main office. The main question that i have before committing is this. Can anyone tell me if i install the Balance 380 at the main site in Drop In Mode will my existing remote VPN connections continue to work? We have remote sites connecting back to the main site via a site to site VPN connection and a bunch of remote users that connect via their PC vpn client. I want to do this peplink transition gradually starting with the main site so i want to know if i setup the first unit using drop in mode will the current remote sites/users still be able to utilize their VPN connection to connect back to the existing firewall that will end up on the internal side of the balance unit using the external IP that they have already been given.

Also, does anyone know if this does not just work with Drop In Mode is there any configurations that i would need to make to get things to work this way?

You can prevent problems with your existing VPNs by using service passthrough support in the Balance locking down outbound IPsec traffic on the drop-in mode WAN. It is also possible to use secondary WANs on the Balance for VPN failover by creating inbound NAT MAPs to your drop-in mode IPs.