Seconding the real AR from calibre innovations. Their spendier option is the borebuddy upper which is very very nice (and what I would buy if I were currently in the market for a .22 semi upper). They are also now doing historic repros in .22 if you want an actual M4 or an XM22 (see their faceache page).
The 15/22 is fine if you want a really lightweight rifle but I wouldn't get one otherwise. Lots of aftermarket parts/upgrades specific to the 15/22.
I've tried the Kriss early on (had broken parts and constant reliability issues which I hear from a lot of Kriss owners), I've looked at the lookalikes which (as mentioned by someone else) are often Umerex or other companies taking a different rifle they make and making cosmetic changes so it looks like an AR but really isn't. Terrible triggers, nonstandard parts, etc.
I have .22 semi auto uppers and .223 straight pull uppers I use on the same lowers, if you go milspec AR you can use the lower for several different uppers (.22, .223, 6.5 grendel, 300 blackout, etc) so if you want other calibres you can save the cost of the lower/trigger/grip/stock which you can't do with any of the lookalikes or the polymer ones. You can also use any of the wide array of standard AR parts on the market for stocks, handguards, grips, etc. You can also get the "Better mag adaptor" and use the S&W 15/22 mags to get proper last round bolt hold open, etc, in .22.
The met also don't seem to count a "barrel and action" (which is what the met have my additional uppers listed as) as a full rifle for the limits before they want increased security levels like alarm that contacts the police, cameras, etc.
