What are the best e-collars and why?

[Jax's Mom]

We're going shopping in the States this week and I was hoping to pick up an e-collar for Jax for when he's older.
We have one for our lab and it works splendidly but they're pretty expensive here and not much selection.
We mainly use it as a an "invisible fence" since we live downtown and also since dog poisonings are quite frequent (in my opinion) so I feel safer when they're wearing them if they're off leash.
Any suggestions on the best brand/model?
Is it best to have one controller and two receivers for two dogs?

Edit: I think I have my answer... I should have searched "remote trainer"
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