1) These, I assume would be unsecured loans. 4% APR is quite low, but this is 4% per day, a considerable jump.
2) The interest paid on savings would not necessarily be compound, it would make more money for the banker if it was not and that is why lots of RW banks use this system, loan out money on a compound basis but average the amount of interest paid to savers based on the average bank balance over whatever term the interest is calculated.
The collateral idea does sound interesting, like a pawn broker, if they dont pay up in the alloted time period you sell the weapon and recoup your losses