I have been using EP with success to upload products in batches of around 400 at a time. Best tips I can give are:

1) Product must have a model number.
2) Model number must be unique.
3) Category name must match existing ZC category name EXACTLY.
4) NO line breaks in product description +
5) EOREOR must be at end of every record.
6) Export as plain text file (.txt).
7) Export settings should be:

* TAB delimited.
* Text qualifier = NONE.
* Include field headings as first row.

If you view the exported file in Notepad there should be no visible delimit between records. I find I can use quotes, commas and slashes in product titles.

8) If you don't have a 'temp' folder in ZC root, create one and CHMOD 777.
9) In Configuration/Easy Populate:

* Make sure temp folder path is correct
* Set date format to d-m-y for UK, or as appropriate.

+ Although EP should handle line breaks in the product description, I had a problem with this. I don't know why. If you have issues, might be something to check.

I confess I haven't downloaded, edited and re-uploaded any data yet.