If you can find a way for it to pass the MOT and are planning to get it remapped, it is definitely worth it. On its own, not so as the car will run lean and not make the power you would expect.
Anything that means the exhaust flows out considerably freer means that due to the scavenging effect the car will draw in more air. The ECU cannot compensate enough for this and so the car runs lean, so if a sports cat frees up the air flow, then yes it will run leaner than it should.
O2 spacers only fool the ECU into thinking the cat is still there and does nothing for the fuelling.
Don't take it there. A map should be bespoke to your car. Not as important with OEM diesels, you can map those relatively safely with an 'off the shelf' map. You can map a car very well with a live drive map but I've not heard of may people doing this in honda world. More of a Nissan/Mitzi turbo practice from what I can gather.
No, you can't remap the stock ecuSo was looking into getting a decat and remap. Now I wanted to find out regards to the remap is the oem ep3 ecuremapable or would I need to upgrade to a Kpro/K100.