I recently bought one of the New Colt .22LR Conversion Kits. The one I received has the roll type tension pin firing pin retention. I'm pretty sure that it is an earlier/older kit as the plastic on the packaging was rather scuffed (presumably from handling), and the vendor that I bought from is known to be a liquidator.
In any case, IMHO (or perhaps due to confirmation bias), the overall appearance of the unit is better than what the pictures depict. I bought the conversion for use in a 1/12 twist 5.56x45 barrel upper, so the accuracy should be reasonably good.
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MHO, YMMV, etc.