p2p is the obd2 ex ecu
p28 is the obd1 ex/si ecu

if you get the p2p it is the same one that you already have
if you get the p28 you will need an obd1 coversion harness

p28 is recommended for tuning because it isnt as picky and a hassle as obd2, you can run test pipes, high flow cats (no 2ndary o2 sensor needed then) hondata, programs (skunk2,mugen,spoon,etc) that can totally change the way the car runs

p2p arent anything special...in fact...I hate them