His ability is somewhat similar to Leela’s.
Either the Corp plays around the ability, slowing their plan down and giving you time, or they don’t play around the ability and give you an advantage to stop their future plans.
Leela is hit or miss, with higher ceiling and lower floor. It’s possible it does stone nothing, the Corp has only rezzed cards. It’s possible it completely wrecks the Corp, opening HQ for repeated Siphons, R&D for repeated Medium, or other such things.
Iain is always Stable. He has a lower ceiling, but a higher floor. It’s never going to do nothing unless you’re winning the game, in which case I guess you didn’t need it! If you aren’t winning the game, you’re getting 8 credits worth of value for free. (Adjusted Chronotype + Hard at Work…) While it isn’t a unique effect like Leela’s, it’s still powerful.
As for ‘better in Andy’, Iain has stronger game against FA, getting two free credits a turn, or making them slow down. Andy is generically strong against everyone. So in that respect, Andy is stronger than Iain against Glacier/RP/IG. Iain is stronger against NBN/FA/Rush decks.