Back in my days of freshly farming Ai higher than 3 I farmed on HBs a bit. I won a lot of upped cards (at least 12+) but I played around 300+ games in the process. I know the numbers are really vague, but it felt I would win an upped card every 30-35 wins on average. Not ideal in any way, nor on par with FGs, but upped wins happen. I would rather see a slightly larger win percentage for HBs, not anywhere equal to FGs, but slightly better odds. I found it was best to grind T50 until you have a decent FG farmer and skip HBs outright. Short of playing them just for the fun of it, HBs just aren't worth the trouble to grind.