Each module/weapon can have ONLY ONE upgrade/time and ONLY one special effect if you are lucky enough to get it. It can be, that if you are lucky and get experimental effect, it will be much more beneficial for you as changed item stats. In current case I only used easy modification for rise my reputation with given engineer. It was lucky draw, updating uses RNG so you may need more attempts to get experimental effect. More cmdrs hates such RNG mechanism, but myself see it make perfect sense that you cannot get perfect stats or acquire special effect easily. Engineering is run on long track, if you want to get updates quickly and on maximum, you can fall into heavy grind and get seriously upset on RNG ... but in ED its common, is UP TO YOU DECIDE what you want to do and YOU WILL NEED dealt with your decisions consequences. ... myself prefer do slow progress from time to time and not aim for "perfect" results at all costs. It helps me avoid grinding and I have much more fun when play ED.