Worked on -27s with both...it's just a mod..glow plugs originally but ignitors were modded in at some stage..either work fine. However only typically got 300/400 hrs out of the glow plugs.
Used to have two spares and a spanner (and the AMM procedure) sealed in a plastic bag in the cockpit...for the pilots to change if they got to a strip and couldn't get a start.