Connecting 120/240 receptacles on the same circuit breaker
This works, as long as your breaker is common trip (most are)

The mixing of 120 and 240V loads/receptacles on the same multi-wire branch circuit is permitted, provided the breaker is common trip (so that a fault on one leg can't be backfed by the other leg of the circuit via the 240V load(s)).  From an electrical standpoint, this is no different from a range or dryer circuit, and the resulting imbalance is not an issue from a safety standpoint.

This is permitted (in the US at least) by NEC 240.4(C) Exception 2:


  (C) Line-to-Neutral Loads. Multiwire branch circuits shall
  supply only line-to-neutral loads.
  
  Exception No. 1: A multiwire branch circuit that supplies only one
  utilization equipment.
  
  Exception No. 2: Where all ungrounded conductors of the multiwire
  branch circuit are opened simultaneously by the branch-circuit overcurrent device.