If you mean the type that install inside the home, I have always heard that condensation is a real problem.

Yes, they're interior storm windows. Innerglass is the brand name.

I, too, have heard that condensation is a problem, but I wonder why that would be any different from exterior storms. We have interior storm windows in a newer addition to the house, but only one window sometimes gets condensation because of the direct sun it receives. It's not to difficult to remove the storm from the inside and wipe down the window if it occurs.

"Not difficult"

No. But will you? The issue isn't one of aesthetics. The moisture will cause paint failure and wood rot on your primary sashes.