Pros and Cons of an external MLT heat transfer system (besides money)

Have to get this idea down on paper, err... yeah. Anyhow I was wondering why not set up your HLT to recirculate hot water in about 50 - 100 feet of copper tubing on the OUTSIDE of the MLT tightly wrapped then insulated? The thing I like about this idea is the length of your tubing/pipe/etc... is MUCH shorter if you run a short hose to the pump then back to the top of your MLT. The major con about this idea is 2 pumps would be required. no biggie if you want a single tier system anyhow but the con of a system like this seems to be money. That aside is this a good idea? Pros? Cons?

I think it'd have to have the mash stirred and recirculated almost constantly to keep the temp the same throughout.

Your heat transfer would be crappy since you have such a small contact area between the tubing and your MLT. Even if you were to solder the tubing in place it would be very inefficient.

As a means of doing herms, I think it'd be really inefficient. But, as a means of keeping your MLT warm (if it's SS) then it'd be beneficial. Maybe you could do this recirc as a means of "stirring" the HLT to keep the water uniformly heated while also keeping your mash temp steady. Seems like heat loss would be the enemy.

If it was an aluminum MLT, it'd be a lot more efficient than a SS one...but still probably much less efficient than the Copper being in direct contact with the wort.