You don’t necessarily need to go loft for loft or size for size, so I’ll give my thoughts.
STi2 Gen2 – nice larger profile club without being “large” or bulky. More traditional cavity back game improvement iron. Silica gel insert to help with vibration (feel) and noise. Not sure the type of ball flight your buddy has or wants, but these are a bit weaker in lofts so you should get more launch, peak height, and stopping power.
TS3.5 – lots of cool tech in these guys. Forged clubs compared to the cast in the STi2G2. Tungsten weight in each club. 4-8 irons get polymer injection. 9-A get the ceramic to help with sound/feel and CG placement. These will be stronger lofts than the GI22 by 1*.
The STi2G2 will be half the price, but the TS3.5 have way more tech and are one of the newest irons Maltby offers. Just a matter of what you/he are looking for.