This was the recommended app to update shipping dimensions for ShipperHQ. I can't image how anyone could use the export for updating a large amount of products. For my needs the export is almost unusable.
With this app the metafield values export in rows instead of columns. My 2600 products exported into 35000 rows on the export. Other apps I found export the same data into 7500 rows.
After a lot of searching I found a better app that exports the data perfectly. It's called Excelify. Excelify is more expensive but it's the only app that exported product and variant data together with metafields in columns.
Some troubleshooting advice:
To prevent a failed import, in both Excel and Google Sheets, convert the ID column format to "Custom Number 0". Both Excel and Sheets have a bad habit of condensing the long ID number which results in a failed import.
Be sure to import and export data in UTF-8 format. This seems to be the standard for metafield apps.

Great app for the price. Not the prettiest interface but it works which is what's most important ...

I tried a few Metafields apps, starting with the cheapest and working my way up...I've now been using this app off and on for a few weeks and, while its output format isn't the best (one row per product per metafield, rather than columns), it's perfectly workable for someone with Excel skills and I find it rather good!
Apart from the bulk export and import facilities (more of that in a minute), the display of information is good and clear. You can select product, collections, whatever else Metafields, to keep things tidy and when you list a single product or collection, or whatever, you're met with a full list of the Metafields applicable to 'whatever you're looking at', along with values. Any or all may be updated on that page, with one 'Save' button. New Metafields may also be entered here (and which then apply to all of that genre -products, collections, etc.). You can also perform a search so you quickly arrive where you want to be.
Simple, intuitive, comprehensive.
The only problem....is that although the app exports a nice csv file, which may be read by Excel and worked on within Excel - the export from Excel (in UTF-8 format, then opened and saved by Notepad in UTF-8 format, to ensure the file *really is* in UTF-8 format, as Excel doesn't do a good job with that) - cannot then be imported back into Metafields2, as there are some 'dodgy' characters hiding there at the beginning of the file.
However...with help from Joe and some experimentation, I've found it's possible to do all the above, working in Excel to do the 'bulk of the job', then open the exported csv file in Google Sheets - and then just save it. This results in a perfectly serviceable, *proper*, UTF-8 file that can be imported back into Metafields2.
Maybe a long winded review, but if it helps anyone with similar problems in the future...I think the app deserves it. It's a good app.