Harabaz Druids are good cards in ally decks, but is not necessarily something you want to spend your time wasting clones on. I don't necessarily know what your current intended win condition is, but I highly recommend Biovisionary (
https://t9k.me/3cj) as your win condition. With this in mind, you should only be using clones to either copy your Biovisionary, or to stall the board until you can find your Biovisionary.
Now putting my competitive thinking aside and looking at this from a casual perspective, I would say that yes, it is a source of high mana. Reliable? I doubt so. As it requires not only one on the field and protected, but also requires clones to copy it is far from reliable. This also means you are turning the fuel for your deck (clones) into mana.... to cast what? More clones? If that's the case then you should probably pick better targets for your clones that have a higher impact on the board. If this is multiplayer casual, then that means cloning whatever the biggest/best creature on the board is. In casual duels, and NOT going for a combo or alternate win con, then have some fun forcing your opponent to fight their own army.
tl;dr: Harabz Druids is inefficient outside of a purely ally deck. The amount of card advantage you lose outweighs the pros of cloning it. You might as well use your clones for copying a card for a combo win or copying the best creature in play. THERE ARE OTHER GREAT AND MORE EFFICIENT MANA PRODUCERS IN THE GAME.