Very slow compared to explorer -- any idea WHY?
I'm not sure what you mean. Opus does not currently support MTP in the first place.
OK, well my Samsung P6800 (7.7 tab) shows as media device (of course using MTP, only choice). When I use Opus to browse content it's PAINFULLY slow. If I use regular explorer it's very fast. There is some reason that D.O. is slow, I just don't know why. I will try some other alternate explorer software and report. Any ideas?!?!
Just tried xplorer2 (which I also own) -- very fast directory display / navigation. NO CLUE why Opus is so slow in this regard.
Do you see the Opus progress dialog while doing that copy, or something else? I doubt that Opus itself is doing the copy at all as Opus itself doesn't know how to write to an MTP device right now.
Does it matter which path you copying from? e.g. Is it slow when copying from a library to MTP, but not when copying from a normal directory to MTP?
Can you show us a screenshot of Opus copying to the MTP drive?
(FWIW, I think Xplorer2 just calls the Windows Explorer copy functions, so it'll probably always do exactly what Explorer does, for better or worse.)
No sweat, give me a little time. I mean Opus just stalls when opening and directory on the Sammy tab (worse if it's got more than 100 files). Explorer and x2 work immediately, so DO is encountering something that it cannot process (quickly). I know it's not the PC, same result at work or home. Screens coming soon! Thanks Leo for the attention, this is really PIA problem 
The Galaxy uses Android so there should be an option to connect it as normal USB-device.
negatory -- tabs only use MTP
I have no Galaxy, but it must have - there're some rooting tuts for it which uses simple USB-connection. I saw pictures showing external storage on E: (which is your data partition), so no MTP. Maybe you need to deactivate MTP-software (Kies?). Normally when connectiong an Android-device it asks which mode should be used when connecting to pc, but maybe Samsung deacrivated this feature and you need an extra app (playstore might have one).
To mention that DO was always much slower accessing devices via MTP - tested camera, windows mobile and other devices and it was never good (really worse when having just some more files and folders). But MTP-access is always slower than a raw USB-conncetion (I have also a WP7 device which uses Zune and it is much slower compared to my Android devices even in Windows Explorer).
Trust me fellas; Samsung tabs CANNOT use normal USB! Even choosing USB debugging - they ONLY support MTP. That said, I will try to take some screen videos of the difference. Give me time, work and life too busy ATM
It CAN, but unfortunately not the way Android normally offers (@Samsung: NoGo!). Have a look here for Galaxy Tabs, maybe it works for you:
http://www.addictivetips.com/mobile/use-samsung-galaxy-tab-10-1-as-mass-storage-device-guide/ or search at XDA-Developers forum.
Alternatively you can try a custom ROM (there're some rooted stock ROMS), but I am not responsible if you brick the device! 
I'm reviving this thread... DO has made pretty BIG improvements in MTP, but it's still not on par with others (xplorer2, Q-dir, or just plain windows explorer). I LOVE DO for life, but there really needs to be some optimization on MTP side. Every single device I own (3 android, 2 cameras) on 2 PC's (NOT potatoes) behave the same... SLOW directory display, very very slow (or failed) copy/move. If I use Q-dir, it never, ever fails. I really want to help fix this issue, how can I?
I have also 3 Android devices which are working w/o any problems and same way like in Explorer (except that DO sometimes displays the device twice). Also copying etc. is fast. I don't have any MTP-tools installed (like HTC SyncManager etc.), just the drivers.
Try setting Preferences / Miscellaneous / Advanced: mtp_enable = False. It will make Opus use embedded instances of Explorer to handle MTP folders, instead of handling them natively. This works better with some devices. (If it doesn't improve things, set it back to True.)