We would try really hard to find something positive to say about the place, though it is not easy. Well, the booking process was quite smooth. If you e-mail the establishment using the 'contact-us' button on their Web site, you get the confirmation in no time (time differences considering). If you have a special request, e-mail "Attention Nadia." Not sure why the reservations were needed though; we have been there on a weekday night, and about 30% of seats were vacant. Maybe it's different for weekends or busier seasons.
Great location, in the midst of the busy and bustling Quartier Latin, opening to rue Saint-Jacques. And there is no entrance fee, but you will have to order something, either a meal or (as in our case) a bottle of wine or other drinks.
That is about all positive we got. The service was quite acceptable, even friendly. But the show itself was a mismatch on an amateurish level. We could still see how Aux Trois Mailletz is viewed more favorably by our fellow travelers; is is still more authentic than the glitzy and corny tourist venues such as Moulin Rouge. But we honestly never felt any difference between Mailletz and some sub-quality bar elsewhere. The 11 PM show opened with a Spanish band of a street-music style and quality; it was followed by a series of bland atop-the-table dancing by Mailletz's employees, who could have easily been the place's patrons gone 'wild.' After an hour or so, and upon finishing our bottle of wine, we started heading home. The waitress begged us to stay promising 'an Oriental dance', whose performers pitifully looked like some bad-taste cruise entertainers.
Maybe it was our unlucky night; we really want to believe so and wish the proprietors and performers the best of luck. But as it was, quite undeserving a visit.

Went there for the live jazz, but we arrived too early (jazz in the basement starts after 11 PM) and we didn't want to eat, so we were seated at the small bar where the unfriendly waitress hardly took notice of us. Eventually had cocktails, which were totally overpriced at 27 Euros!! All the while a strange mix of live classical piano and terrible singing tortured our ears, so we left again quickly.

Food is decent. Service is horrible. Nothing else to add. Be warned. Example: asked for water two times and never got it. Ordered tapas and never got it. Waitress never gave us bread or olives, while the other tables were provided with that and she never came around to ask us if we wanted more drinks.

So often I see reviews that say how amazing a place is to only find out its only mediocre and for once this was not the case. This place was absolutely amazing, as described yes the prices are high. But not much more than in other restaurants in the area, you can get a 1/4 litre of wine for 13 euro. We went around 1130-midnight on saturday and the place was half full, the music was amazing, a mix of the piano player signing and another girl who had the most AMAZING voice. Classic french songs, rent, and english songs. She also stayed and talked with everyone and the entire bar was full of locals. Throughout our trip we have heard some music a few other places all which seemed cheesy and very forced. Aux 3 felt like the real Paris. I'm on a student budget and I plan to eat sandwiches all day just so I can go back here at night. (Stay upstairs with the piano everyone who came up from downstairs looked like they had a horrible time)