You can download the db files using either a web browser or the Mega Desktop App. The App is probably the best method because it requires less interaction to download a large set of files.
To use the app, you have to create a Mega account. You can create a free account by creating a username and password. No payment information is needed.
To download a set of files with the app, click Options (the gear-shaped icon), Import links. Copy/paste a link into the box and submit it.
Because the files are very large, downloading from Mega only works with Chrome and Opera web browsers. I have only tested it with Chrome.
You do not need a login at Mega to download the database install files with a browser. To download a file, right-click on it, select Download, Standard Download. You can select several files before clicking Download. The files will be downloaded sequentially. When you have all the files for a particular group, run the .exe file to install the database.
It would be nice if you could just queue up all the files and come back a few hours later and find them all downloaded. However this will not work unless your PC has a huge amount of RAM. The reason is that Chrome caches each downloaded file and does not free the cached data until you click Save in the message box that pops up as each download finishes. If your PC has for example 8gb of RAM, you will probably get an out of memory message after about 4 of the 2gb files are downloaded without being "saved". For reasons that I don't understand, sometimes you will get that message even if you save every file as soon as it finishes. See below.
If you get a message from Chrome that your hard drive is full, or that you are out of memory, you probably have to clear Chrome's data cache. Go to Settings, Show advanced settings..., and under Privacy, click the "Content Settings" button. Click the "All cookies and site data..." button. Scroll or use the search function to find the entry for Mega, click the Mega entry to select it, then click the "X" to clear the site data.
Download speed varies somewhat randomly between very good and slow. When it is good I can download one of the 2gb files in under 5 minutes. Lately it has been good about half the time.