It looks like a perfectly normal bar, but I can assure you that you'll find exceptional tramezzini, something almost impossible to find in Rome these days, even at the more prestigious establishments. The food is also excellent at lunchtime; I've had their first courses a few times, and they're truly excellent, better than many restaurants. The coffee shop is also good. The restrooms are impeccably clean, too.
Friendly and cheerful staff.
Highly recommended.
The staff are always friendly, the place is clean, the croissants are excellent, and the cappuccino is delicious with a generous amount of foam. Highly recommended.