I chose an Intellitronix digital GPS speedometer for the Porsche conversion mostly because it complemented the blue theme on the Andromeda EVIC display. Click here to see that post. After it was installed and the car was on the road, I began to have second thoughts. It took a long time to lock in on a satellite and begin registering at all, and there was a significant lag in the display when accelerating or decelerating. It was mostly good at reporting speed if you kept it steady, sort of suggesting an average.
A couple of months ago, it gave me an excuse to replace it. First one and then another LED disappeared from the right digit. That made it a little hard to read, but with some imagination you could guess. Twos and fives are a challenge, though. Reading the online reviews, I've learned that this is a common problem.
I have used Speedhut custom gauges in both the eBugeye and the evTD and they have been superbly accurate and reliable. They're custom built and you can configure a huge number of variations; font, text, needle, and background color, even custom logos. I toyed with the idea of a blue palette, but instead opted for a look that's pretty close to the original Porsche gauges.
Even though both our Prius and the Leaf have digital speedometers, I still prefer an analog display with a needle that tells at glance both what speed you're doing and the rate at which it is changing. The Speedhut speedometer locks onto the GPS satellite quickly and registers speed in real time. It's actually quite satisfying and works simply and with no fuss. I consider it an upgrade and don't miss the old one a bit.