I've just installed Drive Bender for evaluation and so far so good.
I've merged my 3 external usb hdd into one big 8TB drive.
I didn't have to waste time moving files in between hdd.  After merging into the pool, existing files and folders were simply group together as one drive. No moving of files in between hdd happened.
Another feature I like are the:
1. Notification it sends out when a hdd problem is detected via the SMART status
2. And the duplication feature which mirrors your selected folder in different physical hdd

Anyway, Drive Bender single home license is on sale now for US$17.95.
But 3 licenses cost only US$24.95 which will result to US$8.xx per license.

If you're planning to buy, let me know so we can buy together at a cheaper cost.