I have a version of myBrickset that "I'm pretty sure" will handle the import/export functionality ok - it's worked fine for my tests, but I can't be absolutely certain I've caught everything. Worst case though, so long as everything is synced on brickset.com, all that will be lost is "favourite", "built" and "gift" status. Oh, and "wanted" count if it's > 1.
The UI's not the best, but it works. From the main screen, select "Export Data". This will export all of your data to a csv file "Android\data\uk.co.otissoft.mybrickset\files\export\export_username.csv" (where username is your username). It will also popup a dialog allowing you to share a copy of the file contents if you wish. I'd recommend you take a look at this file and verify it contains what you expect. So long as the file is ok, even if the import is buggy (it shouldn't be) then I can fix the import and you won't lose anything as the data's still in the export.
To import the data, copy the file into the same location on the new device then run "Import Data" from the menu. It should run very quickly, giving you all of your exported data. Caution though - if things have changed on brickset then these will be overwritten with the exported data, but they'll revert back to the brickset data on the next sync unless you change anything locally.
I've asked Huw about Belgian prices but he hasn't got back to me yet, I'll update the app once he does (assuming he exposes the data in the api).
No worries, thanks for getting back to me! I've improved the UX a little (there's now a screen rather than two menu options, but all the functionality is identical), will probably release an official update sometime this week.
I use that folder because the app has access to it, it's a pain in Android now to get permission to write to the SD card or other folders. I'll take another look though, it's possible things have improved since I last investigated.