//There are no tariffs or non-tariff barriers to trade between the members of the customs union and (unlike a free-trade area) members of the customs union impose a common external tariff on all goods entering the union.//
Correct.
//It's simply a benefit of being in a trading bloc, and a downside of being outside that bloc.//
Whether or not it's a benefit depends on whether the imposition of a particular tariff suits you or not. Unfortunately membership of the Customs Union consigns the members to a "basket" of tariffs, some may be beneficial, others may not.
//What is the point of a trading bloc that ratifies FTAs with third country?//
None at all - if all they want to do is trade amongst themselves.
//The point of a trading bloc is frictionless trade. Now we have friction-full trade.//
It's as full of friction as the EU wants to make it. And since the aim of the EU is principally to protect its members, trade with outsiders is discouraged (see your previous question, above).Normal countries do not behave like that. They encourage global trade, not just trade between themselves.
The pub is the Liberty Bounds, in Trinity Square, opposite the Tower of London:
https://www.jdwetherspoon.com/pubs/all-pubs/england/london/the-liberty-bounds-tower-of-london