I use the GCK60-26bx on my bx2370 and like it a lot. I generally find I need to run it at 3100 rpm or more for sufficient airflow to carry the grass into the bags. The lower you run below 3000 rpm, the more you’ll be stopping to unclog the chute.
Even though I am well satisfied with the bagger, there are other setups out there you may want to consider. I checked my original purchase papers and the bagger was listed at north of $2K, so it’s a chunka change. For giggles I have looked at Cyclone Rakes as an option, and here’s a link that you can follow to see if they might be a viable alternative for you:
https://www.cyclonerake.com/
Guys I know who have a Cyclone rake swear by it, and their base price is in the same neighborhood as Kubota’s bagger. Chief advantage is that they hold a whole lot more than the bagger, by a factor of several (topping out at over 40 bushels), so you can make less trips to your leaf/compost pile and save time. The CR uses an auxiliary engine to create the airflow, rather than running off the tractor rear pto. CRs come in several capacities so, if you are thinking about a bagger, you will definitely want to scope out all your options. Haven’t done any research lately, but I suspect there are additional brands that will do an equivalent job to a CR and give you much greater capacity than a bagger.