I have a BC on my New Holland from Walmart $99. The screen is not large enough to be practical as the machine vibrates so you can only really use it when you are stopped, which may be okay for some situations. I use it as backup for when my neck gets sore plowing snow in a big residential complex--an idiot "wanting my attention" to plow his driveway decides he'll park in the intersection I'm plowing and I side-swiped his bumper. He was drunk, couldn't show me where I supposedly hit him, then said the car was crap (which it wasn't!). On top of that, he paid me to plow his driveway. Talk about dumbasses out there.
Anywho...
As far as using it for a aligning a trailer--it doesn't work well enough to be practical. Since the camera offers no depth perception you have to have it directly over the trailer hitch ball/trailer tongue to take out any quess work. It's like dropping a marble from your mouth--standing up-- into a small container--with only one eye open. Sure it can be done--but how long do you have?
I had the system on my truck's trailer weight distributing hitch which had a vertical member on which I had to mount the camera at a slight angle---otherwise I couldn't remove the trailer. It was shrouded with a piece of 2" angle welded to the member. It still needed to be directly over the hitch ball but I ended up hitching up the trailer, latching it, then using a permanent marker traced the outline of the trailer tongue onto the screen/monitor. The problem was since the camera was so close to the hitch (about a foot away) before you knew it the trailer tongue was in view---and misaligned to boot.
I found my original idea of using an 8" convex mirror mounted on an adjustable stalk mounted to the top rear corner of my truck's camper shell (cap) worked even better. This was bought at the local auto parts and is used by US Mail and FedEx trucks on the rear, and a similar setup is used on the front of semis and school busses. About $30.