Not that I've experience with flex charging, but I've read several places, that flex charging will improve performance from the older packs. As far as I remember, by lowering the internal resistance.
Other than that, the differences seems to be: 8 or 7 amp charge current, auto-start timer, motor run in and of course, discharging and matching. Please correct me someone, if I forgot something.
Schumacher Mi5 - Sanwa MT-4 / RX-462 / KO Propo PDS-2123 - Nosram 5600 X-treme Saddle Pack - LRP SPX Zero/X12 17,5 - Nosram Stealth Touch Evolution - MAAS SPS 9250