I work for Horizon Hobby, and am on Team JR....
FWIW, personally, I run 5 cell unregulated on all my jets... No problems... Many HH employees also do this.

I think it is a personal choice... If you are careless... for example....
You rig something with a stalled servo, or have a gyro gain somewhat high, you may run into problems faster than you would on four cells... I choose 5, for the power, speed, and voltage headroom.

Regulators are fine, but without doing my own testing... They may possibly generate rf noise (since they may use square waves that can have some high frequency components), let us know if anyone has tested this, and they are something else that can fail.... more wire, etc.

Therefore, personal choice.

David