I just bought the official Honda tow kit (coolers, hitch and wiring harness). If you price out the parts (hitch, draw bar, pin, wiring harness, trans cooler, etc.) it isn't a whole lot more than typical after market stuff - probably $300 versus the $450 I paid for Honda approved stuff.
I'll be putting all of this on this weekend - it doesn't appear to be too difficult. A number of threads describe the installation.
By the way, the trans cooler is always a good idea. I have burned out transmissions in full size vans when towing as low as 1500 pounds. It all depends on the conditions and wieght you are towing. Add in air conditioning and strong winds and any towing is hard on the trans.
I, too, struggled with this decision. I was quoted a figure of $250 to install a hitch, generic trans cooler, and wiring harness. Another thread in here describes the legalities of warranty. Basically, per the thread, Honda cannot "duck out" on the warranty unless the modification can be proven to have caused the damage.
I just figure the extra couple hundred is worth not having to argue if anything goes wrong. Plus, everything fits and mounts where it is supposed to. I burnt one transmission on a full size Chevy simply due to a hose kink in an aftermarket trans cooler - I don't want things like that to happen here.
I want everything done right on my new Honda!!!