Props to you guys for putting a complete tutorial on that and not keeping it for you. Cheers!

Thanks! Internally we use more sophisticated system required by larger scale to support higher volume and concurrent connections from multiple clients, but for smaller scale limited to one person or a small team, everything described on our blog should be enough.

Wouldn't this mean that you're bandwidth constrained by the data plan associated with the SIM from the mobile carrier?

Yes, but we have so many plans and actually many of them are unlimited. We also track data usage and can either add extra data package or a SIM card gets excluded from our proxy pool.