I shopped and bought my BH last year... here's some tidbits that may be helpful.
Bradco makes heavy, commercial-duty hoes, with a price to match. Sounds like you need something like that, so the Bradco is definitely something to consider. I came close to buying the 509 last year, but finally went with the OEM hoe from my Kub dealer due to dealer support concerns. My hoe (4560) is an older design for the L10 tractors, but it's every bit as heavy-duty as the Bradco... actually seems closer to the larger Bradco 609, so I have no doubt it would stand up to severe duty. Just from looking at it, the boom and dipper on the BH90 seem a bit lighter than mine, but I wouldn't have a concern with working it hard.
Both Kubota and Bradco have a close, solid subframe setup for the L series. Part of the subframe kit for my tractor was a whole new fixed ROPS assembly, which is 6 inches taller than standard, so the BH operator does not have headroom issues under the ROPS. Added height probably also increases rollover protection. Don't know if this carries over into the L30 - BH90; if so check any garage door heights for clearance.
I think Bradco lets you keep your 3 pt arms attached when installing the hoe, although it's a simple 5 minute job removing them with the Kubota.
Bradco will give more options such as pto pump or tractor hydraulics operation; the BH90 is only available run from quick connects.
Bradco may have better resale if you ever decide to dispose of it... with another subframe, the same hoe can fit another tractor. The BH90 is only for Kubota.
My 2 cent opinion is that you can't go too far wrong with either choice.
