CB750 Cafe Racer Fan - the SpeedHut GPS Speedometer comes with a hotwired GPS sender, always powered (pulls very little juice, never had a problem with it) so GPS is ready to go once you start your bike. I routed it back to my side covers and stuck it to the inside of it with some Velcro. They suggest not mounting it directly under steel, so that's why I chose the side cover.
Their custom gauge builder has worked great for me on my computer and phone, try another source!! It really is nice to get them exactly how you want. Also, keep digging in their products
they do offer them with idiot lights, and will even out place little oil/high beam/engine symbols next to them if you ask nicely!
Edit: Yes I ran the GPS speedometer all summer last season and never had any issues. It (seems) extremely accurate, no delay in the needle speed for speedo or tach. I liked it so much I ordered different gauges from them! They're shipping tomorrow. You lose signal going through a tunnel or under some large overpasses but that never bothered me, they tell you on the site that will happen.