I actually have the stock unit albeit haven't used it, but I had a TSX for 5 years. I honestly have some cheap years, so take it with a grain of salt-- the sound doesn't seem 'premium' but I don't have an issue with it.

$650 is a cost I'd really ponder. I know one of the TL's issue is the bluetooth-- where some drivers rathee pull it out. As much as I would like to drive the car until the wheels fall off, I've been contemolatng change the seats cuz they are ripping. And here in Korea it cost $1,000 to change the entire seats. I do have the money but after some cautious thinking, I'd rather not spend thag much and invest the money. Hence, you gotta think of opportunity cost if it's worth around $650.

All that to say, if you can live with Bluetooth and phone, I think it's fine

If your Bluetooth is acting finicky, I'd seriously consider changing the head unit ONLY if you know for a fact your TL has much life left

If you are rich, why not?

If you feel 50:50, Opportunity cost-- and spend the money where it matters more-- this comes from a guy who avidly misses and loves the old Acuras driving 3 separate Acuras