Good speedometer needed

I'm another Wally World, $12.00 cheapo user. They seem to work just fine with the exception that on rare occasions they reset themselves. Maybe once or twice during a riding season. You're right about the wireless kind. They're susceptible to RF interfernece from the ignition system but the wired ones aren't as long as you keep the sensor wire away from engine components. I usually mount my CDI to the seat tube, not the down tube and keep the speedo wire away from the kill switch wires and clutch cable.
I had one that was dead out of the box but four others have performed perfectly.

As for programming you can get the number a couple of ways. Carefully measure the circumference of your front tire, convert to millimeters and that's the number. Another way is to make a mark on your tireand on the floor where the mark meets it. Roll the bike forward one wheel revolution (keep the wheel straight, no turns). Mark the floor again where the tire mark hits and measure that distance. That's the number, again in millimeters, you program in.

One critical aspect is alignment of the spoke sensor (magnet) with the little arrow on the front of the pickup that clamps to the fork. They must align perfectly and as close to each other as you can get them without contact.
Tom