It is a really convenient and economical way to pre-heat.
I never had to go more than 45 minutes for a toasty engine, oil bag, or other components - it got ALL the various metals to the SAME TEMP (or nearly so) facilitating a smooth start!
Still have it, though now, since the airport installed POWER near my spot, I simply "plug in" to the Reif System. Still kept the DRAGON, however!