I may just be a dumb homeowner, but even I can figure out why the only place the spine-fins get used are outdoor coils, and not refrigerators, indoor coils, etc.

You can hose (or if necessary, torch) off an outdoor coil. The spine fins seem to clean pretty easily this way. They are efficient, long-lasting, and easy to clean with the tools available to somebody servicing an outdoor coil.

Neither of those is an option for any indoor coil. You can't hose off the back or underside of a refrigerator, and I know I would be a little wary of some service tech lighting dust bunnies on fire in my kitchen. You clean a fridge coil with a brush and/or vaccum. Yeah, that would certainly slaughter a spine-fin.

Trane realizes this, which is probably why you don't see spine-fins in the indoor coils that Trane makes.

Since it uses louvered panels, the only way they are going to get damaged is by poor servicing. Many (most?) brands of plate-fin coils seem to use just a cheesy WIDE open wire grid to "protect" the coils. The next door-neighbors kid playing with a basket-ball can flatten a pretty decent patch of those things.