When downloading files using the Downloader Online, there is no file size limit. Whether the file is 10MB or 950MB, you can download it.
There are a few things which factor into this. First, it depends on your Internet connection. The faster your Internet connection, the faster the download. Second, it depends on the size of the file. The smaller the file size, the quicker that the download will be.
There are no limits placed on the number of files that you can download daily or how many times you can download a single file.
Yes, the Downloader Online is compatible with both the Windows and Mac systems.