The Letus Extreme is well reviewed and folks have been using them for long enough to prove their reliability. That said, the addition of extra stuff always adds complication (backfocus adjustments, needing external monitoring for critical focus, etc.).
For better or worse, adapters and AF are mutually exclusive (unless you are buying something with the Birger EOS mount… they are spendy though). Also, if you are using EF glass, you won’t be able to control the aperture from the adapter, so you’ll need to carry a stills camera body with you ‘on set’ to make adjustments.
If you are shooting with that excellent B4 mount Canon glass on an XL2, why not just grab some ND and CP filters, open the lens as wide as it’ll go and move back from your subject to get shallower DOF?
