No problem with a Koso Tach - another member recommended it to me a it took all of a hour to install. Simply remove the seat and gas tank, connect 4 wires frorm the tach harness; one to the ignition via a supplied splice, two to the battery terminals, and one to the coil with an included splice. Reinstall the seat and tank (for a longer and more comfortable ride) and VOILA! The programming of the tach is MUCH more difficult and poorly documented, but included,so check out this thread with photos from the old Forum. I could not find a way to upload my photo from this machine at work.
I used a product called tiny tach. As I remember they make ones that refresh every 2 seconds or every 1/2 a second. Also doubles as an hour meter. I'll try and take a picture of it later today on the bike. Bought from a website involed with DR650 mods I believe. It came with a nice anodized alum for the handle bar bracket. Looks like this product.