Rodrigo gave an excellent tour of San Telmo! The tour lasted about 3h 15m, however there are free bathroom stops along the way (one at the meeting point, and one approx. 1h 15m into the tour, plus there is a 10 minute drink/food stop about 2 hours into the tour where obviously if you purchase something at any of the cafes you can use their bathroom).
Rodrigo is very knowledgeable about Argentinian history, and delivered the info in an entertaining way, keeping up a good pace, and not making you feel overwhelmed by it all.
We started at Museo Nacional del Cabildo and ended at one of the entrances to San Telmo Market (after strolling through during the tour), so you have a chance to go back after and look through at a leisurely pace if you want.
We had a great time on this tour, and it was lovely that Rodrigo offered up suggestions for bars and restaurants as well. It was also helpful that in addition to accepting cash and PayPal tips, we were able to tip via the Freetour app. We recommend this tour to anyone interested in learning about Argentina's history, as well as current issues in BA, specifically in San Telmo neighbourhood.