Other than the payback (ROI), what else should we consider?
Most customers only look at price, and that's misleading and potentially expensive. A quick payback may not be a great investment if the solution has a short life span. With areas like solar PV and LED lights, there can be a 10 times variation in the expected life of the product or components. For the novice it really is buyer beware.
Some brands make it very difficult for customers to claim on their product warranty. Buyers should look for a market-leading product warranty and ensure they know the reputation and reliability behind the brand. Unfortunately, the likelihood of getting your product warranty honoured directly by an offshore manufacturer without an Australian presence is low.