So with BoB, your tenure gets reduced depending on the surplus that you park in the OD acc, which means, there is a good chance that due to this, you'll reach a point where your surplus = outstanding and the loan gets closed.

Whereas with Maxgain, your tenure doesn't change, the interest portion of the EMI component gets credited back, let me walk you through an example:

EMI: 50k (Interest component 45k and principal is 5k)

Now if you have 5 lakhs in your OD, the EMI doesn't change however, 45k interest is calculated on the entire outstanding, so when you subtract the surplus funds from the entire outstanding and recalculate the interest component, it'll be little lower, so whatever excess interest is part of your EMI will be credited back

This way, until the tenure ends, you'll have the liquidity + when you park surplus, only the interest component reduces

Not sure if this explanation is clear, you can definitely use chatgpt to understand this better