I can't speak for anybody else but cleaning out a tank, scrubbing the old resin, filling with a different - transparent or coloured resin - is annoying when you only have one tank. Similarly when having to change the FEP film, not being able to have a print running while repairing a resin tank is also annoying. To me anyway. So, best thing, buy a couple spare tanks. The advantage here with the lids and soft secure storage these come in, is that I can leave a resin in the tank for a while until I need it. Then just swap the tanks rather than all that time consuming cleaning and fiddling. Also, if I do need to change the FEP, I have a spare tank to continue printing with until the original is ready. These are perfect fits for the Mars 3 that I have, match the original tank precisely and are the same quality. Only thing I would suggest is that you replace the screws with the stainless ones available in this store. Much better screws than the default ones. This is a great product at an excellent price and for impatient types like myself, an absolute god-send. Couldn't live without them - not peacefully anyway.