Welcome here.
Looks like a reasonable circuit, though you dont show ground connected on the feedback rectifier.
The efficiency depends on the output power, the circuit itself will use some energy, so if your only pulling a watt or so it will be inefficient.
U4 needs a decoupling cap, in fact all ic's would benefit from one.
Also your switching the fets hard a resistor inline with the gate to control turn on time might improve things, 10 - 22 ohm is common.
I'm not sure your method of feedback is that great, using one of the op amps on the '494 might be a better idea, or possibly pin 4 the dead time input on the '494.
Still not a bad try, with a little tweaking it will improve.