On this new Mamba Max pro 1 cell, since there is no BEC, do you really need a BEC to use this ESC?

It also rated to run 1-6s, if you run 4s, do you need BEC>?

What is the effect of not having the BEC>?

I run the Mamba Max Pro 1 cell in my hyperdrive oval car. The only thing I did was use a SMC 2 cell 430mAh receiver pack and it works flawlessly.

You will need to use a BEC with 4S or a separate receiver pack. There are no receivers or servos that can run on that high of voltage. If you were only running 2S you could get away with running it directly to the receiver and using an HV-capable servo (that's what I do) but anything higher will require a BEC to regulate the voltage.

"No BEC" literally means that the ESC will not power your receiver directly. You'll need a separate power source for your receiver and servo(s).

-Eric