I have epson and I have been buying their non-epson replacement cartridges for a lot cheaper! I don't buy the original epson ink cartridges anymore because they cost so much. I've been using the replacement cartridges for awhile now and I don't think I have had any problems except my printing quality has declined but I'm not sure is it because of the replacement ink or just because my printer is old.
Probably the ink. Your key word is cheaper. There are equal but less expensive inks. There are cheaper inks, especially in the dye side, that are diluted more than OEM.
First of all...is there any difference between real genuine printing ink and the no brand replacement cartridges? Do they damange your printer or are they exactly the same?
Some are pretty identical. I have used MIS in one printer from the day I opened it, but used Epson drivers for two years. I just profiled it to newer ICCs with very little difference.
Some cause head clogs. It all depends on brand.
Second of all...do printing quality delcine after you have had the printer for many years?
Not really, unless the heads are clogging or not firing. Heads (Epson) either fire or they don't. There is no decline. Clogging or non-firing parts are immediately noticeable as either banding or an extreme color shift.
Canon, HP and others use different ways of dropping ink. You didn't say which printer you have.