I think glow plug wear is ingreased if you have battery connected all the time. Platinium coil resistance will ingrease when it heats up, either by current or catalystic reaction of methanol. So constant voltage is better and simple principle.

Years ago during nitro shortage I installed small microswitch next to the throttle servo and used round servo wheel which I filed "bumpy" so it made contact around 1/3 from idle. Just one 1200mAh NiCd and I was able to even start engine with sysem first two flights. Then changed the cell or sometimes quick charged between flights. About 80 gram sacrifce for reliable idle.