Are aftermarket tachometers reliable?

I have two in separate older vehicles and I have never had a single issue with mine. I too like knowing how many rev's my engine is making. Both were straight forward and easy to hook up, using a lead off the coil and selecting how many cylinders on the tach it self. Most come with good instructions and I hooked mine up so even the dash lights would turn on the back light in the tach. All the best, Hans