The integrated VPN client in Windows Mobile 6/6.1 is a standards based client, I don't know why you wouldn't want to use it? I currently have Cisco IOS Routers & PIX Firewalls configured to work with the integrated VPN client in Windows 2000/XP/2003/Vista as well as Windows Mobile 6/6.1. I have disabled the PPTP stuff on the Cisco devices and only use the L2TP/IPSec with 3DES but it all works perfectly.
It took a while getting it working effortlessly but it does now
Setup on the Client side is simple and easily supported - no worrying about 3rd party apps, I can't complain about any of it (not now anyway, at the time of testing and getting it all working might have been a different story.....).
Plus Cisco don't have a Windows Mobile VPN Client?
Andy