OMG!! So glad you asked before buying.
STAY AWAY!!
They do swell. They swell and break off easier than the regular ones. I sent them the piston with their glowplug stabbed into it to prove it to them. Yes it destroyed the head and the block too. And they denyed it so much they wouldn’t even do a refund on the glowplugs.
Buy only AC Delco 60g or Bosch 80034 (there is a longer number with them too, but that is the one I remember and ordered them by. Both of these plugs are the only self regulating plugs available. Self regulation is the only way they stop from swelling- which when it sweels to much is how they break off.
Leroy sells the plugs, and a small solenoid that attaches to the controller. You just run a single wire to it from a button or switch you control for when it is way cold and needs a second cycle, yes you will loose an extra 5-7 seconds more on the coldest days when doing second cycle. Added up over 300,000 miles of starts you are WAY ahead of replacing an engine for it.
Something that folks in colder areas really should focus on is the powermaster starter. It cranks the engine so much faster than the regular one, and crank speed is huge.
Please NEVER use starting fluid. Outside the obvious blow the idi diesel apart problem, the fluid as it burns actually has a chemical process with the metal of the glowplug and form crystals on the plug, causing them to fail much sooner. Sometimes first use.