Curious regarding dhp

Now that they’ve been used for quite a while now, does anyone have an idea on the lifespan of deep heat projectors?

I’m a big radiant heat panel advocate, but if the dhp have long usable lives I’m very tempted to start switching to them.

I’ll be building a few 4’x2’x16" enclosures and thinking I’m going to set them up with dhp instead of panels.