We have had an increasing number of JMeter users since we announced support several months ago. We have been adding minor big fixes and improvements along the way as we get feedback.
We recently made a couple of changes for large JMX files (20MB was the customer example) and large set of config files (215 was the customer example).
We just deployed the ability to upload and expand config files (supports .tar, .gz, .tgz, .zip). When uncompressed it will be in the same directory as the load test runs from. When you upload something with one of those extensions the checkbox text should change to ‘expand’.