When looking at espresso gear it makes sense to ask where money spent contributes to better espresso and when it does not. The tamper is a place where many people focus too much of the energy and money. There are some amazing tampers out there. Reg Barber makes a custom made tampers that are quite pretty and feel great. They cost about one hundred dollars. Torr makes even more expensive tamper that is also stunning and incredibly detail oriented. They are great works of art that are fun to use. If you enjoy an object of beauty they are interesting purchases. On the other hand, a cheap tamper that fits your basket (many are available for around twenty dollars, for example) will work just as well, but will not be as pretty. I confess I do have a weakness for tampers and while I do not own an expensive tamper I make them for myself as a hobby, buying a cheap tamper and using the piston and creating the handle myself.
The tampers that usually come with even expensive machines are usually a little to cheap and especially odd because they usually are not big enough, but if the tamper is almost the right size for the basket (within four to five millimeters) and usually if the piston is made of metal then after that the major difference is more about aesthetics than anything else.
The key to tamping is creating an even flat bed and being able to use the same pressure every time. You can practice with a bathroom scale by putting the portafilter on the scale and tamping. If you can do this with your tamper then the tamper is good enough. For that matter if you can do this with the bottom of a jar then your jar is good enough.
Thirty pounds of pressure is the official weight people are suppose to tamp with, but most agree this is not essential as long as you are consistent. (If you are not consistent the espresso will sometimes be overextracted and sometimes underextracted.