Sadly on aikiweb it's near impossible to have a viewpoint on this unless you've trained with Mike Sigman or Dan Harden. I think this is unfortunate as it excludes a great many people from joining in the discussion for no particularly good reason. While I'm quite sure that what they have to offer is excellent (I was looking for it in various places outside and inside of aikido about ten or so years ago) they aren't the only game in town,
I'm genuinely interested in which other IP/IS methodologies you feel are worth investigating, since though I'm admittedly Dan-centric because of the close-coupling of Daito-ryu and Hakkoryu, I've found something of value in every methodology I've come across so far.
Dan and Mike are not the only games in town, but they have, more than most, expressly sought inroads to the aikido community; and their methodologies, while different from one another, remove the need for guesswork and interpretation (though the development of the ability to use intent in the prescribed manner is greater than just about anyone bargains for going in). I Liq Chuan is similarly systematic and geared toward a western audience.