Pros:

• GentleWasher is the best solution to cope up with electricity crisis.
• Good in emergencies.
• Best for the garments, like woven garments, which cannot be washed with normal washing machines.
• Almost zero maintenance required.
• They're offering 30 day full refund guarantee, you can also get shipping fee back.

Cons:

• As the hunter mentioned, it requires user's labor.