About the system of reiki itself:
I find it...gnawing that these people get away with selling these 'attunments' for hundreds of dollars, whats more gnawing is that people actually buy them!
But that aside, I have out of curiosity scryed/scanned/and experimented with the components of reiki under astral test settings briefly for a time, and I guess I can give a quick rundown of some of my (surprisingly decent) results that I can remember still. I did this to see what inherent power these sigils hold, or if its mostly just intent and belief in the system. Personally If found that one needs no 'attunements' to work with reiki or the systems tools, its mostly just basic spiritual/energetic system development that is attained by working with energy, the attunements that are part of the system could honestly be done in seconds by anyone that has ability in energetic healing and strengthening of systems to give someone a little boost in astral and mental balancing and development to handle the energies required to heal. The sigils themselves do seem to correspond to some pretty basic archetypal functions, and I think could indeed be of some use if applied properly. However I would not pay one penny for an initiation that can be attained at will by your own self. Spend as much time as possible for two weeks, the first half take 7 days each day meditating on a chakra from the muladhara to the sahasrara in sequence, then spend a week meditating on the flow through the two connecting meridians that runs from the perineum up the spineal cord over the head down the nose and to the roof of your mouth, and from the tip of your tongue down your throat and down the centerline of your body connecting back at your perineum and you basically have just done more for yourself most of those "official" workshops could do imo.

Cho Ki Rei
Upon the first time looking at this picture I got a momentary slight dizzy feeling as though it pulled my attention towards it. The designer of this sigil seemed to have in mind a character that would inherently focus the energy condensing caused by attention. I reached my mind out and touched it, I got a sense of a goldish light emanating off it in waves whilst giving off a D scale tune with each wave. (After the experience I went and looked up some correspondences and found out the D tune represents Condensation and materialization Qabbalistically interestingly enough.) I opened the sigil as a gate and entered into it, I got the sense that while on the outside it seemed to pull my attention, when I activated it in such a manner there was a considerable boost in the amount of energy that is gathered into places that I put my focus onto. This I realized after corresponded quite well with the overall nature of the sigil itself when I talked to someone who has knowledge of the mainstream system. It also seems to have a nack for drawing the maladies you are healing into itself quite well almost like a quarantine black hole. Uses of this sigil could potentially be many, while scrying it I got a series of mental flashes that seemed to be slight modifications of this sigil to treat specific physical problems, mostly it involved adding certain other characters, I would draw them up but anyone can access them. (this i found out goes for all the sigils except the final "master symbol")

Seiheki
This sigil was odd in that as I was reaching out to it with my mind in an 'initial probing' it seemed to respond by reaching out to me. It entered through my awareness into my mental sphere and seemed to... "Shine light on the darkness" I noticed that I began remembering lots of things that I had been forgetting/procrastinating and had a huge urge to get to doing them. Its influence didn't seem to extend much farther naturally than "loosening up" my personality a bit, letting me see myself better if you know what I mean. After experiencing this I pulled back from it and decided to try some practical application because of its peculiar properties. The only real spectacular result I received by using casting this sigil "barebones" was upon application to a servitor, it seemed to take on sharper sentient qualities. Almost like a micro-evolution stimulant for the psyche.
From what I've heard while the first sigil is used to heal mostly physical and energetic problems, this sigil is used to heal emotional and mental problems among other things.

Hon Sha Ze Sho Nen
I was compelled to look up what the translation of this was and it seems to mean "the budda in me, meets the budda in you."
This one seems to differ in that the power is in the concept behind the phrase of this sigil. It stimulates a psychic bond directly between peoples akashic centers. Simply put it seems this sigil helps those who are not proficient in this area to do distance healing easier it seems.

Daikomyo
This is known as the "master symbol." It seems to be used to heal the deepest levels of ones being, as well as representing the highest personal qualities one can aspire to attaining. I got the feeling when experimenting a bit with this sigil that the archetypal concept behind it is "true adepthood." All in all I think it would make a good daily meditation focus if you plan on following this path.
These sigils didn't impress me overtly, I think that if one were to meditate on it a bit that personalized sigils could be constructed that could be more effective. However the simplicity of the system of reiki itself which does seem to compliment any other path quite well is very appealing. I get a bad taste in my mouth when I think of the prices people pay for to learn this simple paradigm though.
Honestly if anyone wants a "reiki attunement" for stronger energy flow and pathways on all levels or what have you I would be happy to do one for FREE just to spite the hustlers, but no single attunement would help as much as pure meditation on developing your own being and why these things work would.