For The Experienced Only

I wouldn't trust it either. When working with a straight siphon without an emergency drain you're risking floods IMO.

As the plumbing breaks in and develops a slime coat etc, or if a little snail decides to go down the plumbing, you will get slight variations in the amount of flow, or perhaps your return pump(s) will have slight variations in flow as well.

On my tank's plumbing which uses a siphon I have a backup drain that is above the water level of the main siphon drain and even though the system has been up and running for over a month I occasionally find a little bit of a drip coming down my emergency drain. That may have something to do with my plumbing as well which is slightly unorthodox so your mileage may vary.

I really would not trust trying to balance a return pump with a siphon drain without backup measures in place, just sounds really risky to me.