I got 2 GSR and d15z1 oil coolers a while back, just had other things to do on the car first, then forgot. Technically the GSR's is called an oil cooler, and the Z1's is an oil warmer. I'll explain...
The GSR uses thicker coolant tubes, maybe 1/2" or so. Inlet is fed from the bottom of the water jacket, between cyl 1 & 2. The coolant isn't very hot right there. The Z1 "warmer" uses 3/8" lines or so, and is fed by the water jacket farther up behind cyl #2. The Z1 is probably an easier add-on, since it uses the smaller tubing usually used for the FITV and IACV.
The theory is to heat the Z1 oil quickly, and keep it at a lower viscosity (hotter) for reducing drag. They probably didn't keep them on the HX because the VX was intended more for short city drives, but some hippies had other ideas. On the tests I've seen on viscosity, it helps more than you may think. The GSR intends to warm the oil a bit faster so you can "crack" vtec with less warm-up time, as well as keep oil temps down for hard driving. I've not compaired the fin differences between them, but tube size is all that seems different.
Overall it works well since you keep oil at a consistent temp, rather than overcooling it. Unless you failed at choosing a fan, your ECT's will never be over 205. Oil can get past 240+ in a tracked NA honda, worse with a turbo. It warms it faster, and keeps it cooler. I used to remember what other cars came with them, I think some turbo mazda motors and some VW's.