If you are a maintenance freak, the shared reservoir is no big deal. Most people are absolutely not maintenance freaks i.e. bleed before a track event and bleed the after a track event
Most people that have a good maintenance program will bleed before and drive on the fluid until the next event. For the vast majority of C5 owners the separate reservoirs are a good idea.
Is fluid more important than split reservoirs?
Boiling point ranges
Dry boiling point Wet boiling point
DOT 3 205 °C (401 °F) 140 °C (284 °F)
DOT 4 230 °C (446 °F) 155 °C (311 °F)
DOT 5 260 °C (500 °F) 180 °C (356 °F)
DOT 5.1 270 °C (518 °F) 190 °C (374 °F)
When rotors glow they are 1,000F Again, most C5 owners will not drive so hard as to get their rotors glowing. When you look at the wet boil points of ordinary brake fluids it would not be at all unusual with moderately hard brake use to see fluid temps in the calipers of 311F or too close for comfort to the wet boil range for average fluids.
The SRF is hands down the best fluid and comes at a super premium price. The Motul RBF600 is reasonable at $15 a bottle and I would say mandatory for a daily driver that will see some AC and Road Course use.