If I remember right, KS9s are Phonak Marvel 90. I see on the Flagship listing a Phonak Sky M90. That may be the same, but I can’t be sure.
Things to add to your comparison:
CostCo provides domes free of charge. And the wax guards also. Tru Heaing?
If you happen in to CostCo to shop, if they aren’t busy they will do a free cleaning while you are shopping. Takes about 10 minutes, if you live near enough you can just stop in for them to clean the pair, even if you aren’t shopping.
To get the CostCo warranties, you do have to maintain the CostCo membership. $60 per year. Would he have the membership otherwise, so he is getting that anyway? And if you put the purchase on the VISA to extend, you are talking a 5 years membership.
Put the purchase on the CostCo VISA and (I’m not sure if this works with the $60 or you have to get the $120 membership) you get rewards. You need to do just a little bit of shopping to make a good $60 rewards check that first year, with the hearing aids purchase on there.
CostCo offers the PerfectDry Lux dryer, $40. Get that when you buy the hearing aids, bump up the rewards check. What will he do for a dryer at Tru Hearing?
Batteries at CostCo are low cost. Where will he buy batteries if he gets the aids at Tru Hearing? (I have no idea how far he has to travel to CostCo, or if he already has a CostCo membership. I got the membership specifically for the hearing aids. I have a 45 minute drive one way to the nearest CostCo. So I buy a 4 month supply of batteries at a time.)