the difference comes from head tracking. without it, the convolution will not need to change based on where you turn your head, so it's significantly simpler to use/apply. not how much we rely on head movements to locate sounds, that seems to be fairly different from people to people, and so is the change in experience from not having it(fancy way to say that I don't know how you would feel but I know how I do ^_^).
with custom measurements from an actual room turned to a profile for OOYH, the result is going to be the very best, most elaborate "crossfeed" effect you can get. including such effect properly applied to multichannel tracks. so it's already a pretty big leap toward custom speaker simulation. minus head tracking.
I'm tried to make my own version using HRIR found online and testing each one to try and find one that would work ok for me at least at 30° on each side for stereo. and the result subjectively is a good deal better than crossfeed(and IMO leagues above traditional headphone stereo distribution of sound). so with a measurement done on my very own head, I would expect even better results. which is why I jumped on a cheap Realiser when it came on kickstarter. because I was already wondering how to do that at the time and the A8 was 3000euro in France, which is more than I'll ever put in any single audio equipment no matter how convinced I am of their purpose.
OOYH's included profiles don't really do it for me, but no universal solution ever does, so it's reasonable to assume that I simply have a body/head altering sound in a way that's too different from the ideal average model of human(or whatever was used as model for the recordings). no luck for me, but based on feedback, it's also fair to assume that many people get or come very close to getting the same very close to ideal experience I have with my DIY stuff(plus the room from cool places instead of my half baked artificial reverb I add to the HRIR from an anechoic chamber). getting custom measurement is only going to be icing on the cake for those people who already have great results as it is. while it's going to be a literal necessity for those like me who have a weird head ^_^.
no return. the risk is massive every time we jump onboard such projects, and as a rule I agree with you that it's a bad idea to pay for something that doesn't exist. because of the risks, but also because men are going to be men. once they already got the reward for a job, most will lose their motivation. any gamer knows how pre-commands are basically a method for the consumer to shoot himself in the foot. it can be very similar for kickstarter campaigns.
on the other hand when you dream of having a specific product and the only guys who wish to try and make it, lack the funds, what can you do? the options are for the product to probably never exist, or to take a chance and support those people with our own money and hopes. those aren't good options, but sometimes they're the only ones we have.