i've used and been certified on both these platforms. neither one of them offers a true Custom WaveFront treatment. the Nidek can do custom in Japan, but their more advanced laser never got FDA approval in the US, because they're selling so few lasers here it wasn't worth doing the FDA trial in the US, as that costs over $1 million. the market share of Nidek for LASIK in the US, by the way, is about 1%. meaning 99% of the procedures in the US are done on a different platform. the only reason to use a Nidek laser in the US now is that it is cheaper to use it than most other lasers, because it doesn't require a royalty or "click" fee. so doctors or centers wanting to cut prices below the competition often use the Nidek, as that's one way to reduce their costs. i used to use a Nidek EC 5000 laser myself, but that was way back in 2000, when that was a state-of-the-art laser.
in terms of the Allegretto, that, too, is not a true Custom WaveFront platform. it is so not true wavefront, that FDA prohibited that company from marketing it's laser as "WaveFront" and required them to tack on a modifier: "WaveFront-OPTIMIZED" this is like USDA requiring the makers of Velvetta to call their product "cheese-FOOD" or makers of soy "milk" to label their product "contains no dairy product"
the Allegretto platform takes a true WaveFront scan, but then does this weird thing where it then matches your scan against it's internal database of a few hundred profiles, and then chooses the "best fit" sphere. so your treatment is optimized, but not truly custom. in other words, for every laser treatment done on the Allegretto, there is someone out there, somewhere in the world, getting an IDENTICAL treatment. the market share of the Allegretto laser in the US, btw, is about 5%
my preferred laser platform is the VISX, because unlike the above laser brands, it DOES perform a true custom WaveFront correction. it takes a unique wavescan of your eyes, each of which is like a fingerprint of your prescription, so that no other person ON THE PLANET has the same scan. then that scan is saved in the computer, and transferred with a flashdrive into the VISX laser. it is a true custom system
VISX is by far the dominant laser in the US, with about 75% market share. this means there have been more eyes lasered on the VISX platform than all other laser brands--COMBINED
you can get excellent results on either a Nidek or Allegretto laser. just be clear that neither are true custom wavefront platforms. if i were getting my own eyes lasered (i was the 1st LASIK surgeon in NYC to get LASIK himself, and i did it on a VISX), then i would choose the Allegretto over the Nidek, if i were being lasered in the US. outside of the US, i might choose the Nidek, especially if i were in Japan where they have the newest version w the upgraded hardware and software
don't worry, you can and probably will have excellent results, no matter what platform you choose, they are all good, just some are true custom, some are non-custom, and some are pseudo-custom