When choosing a lightweight scale you need to consider the power source.
You will get three choices.
Battery: This is a good option and if you go for this choice, please ensure that the type of battery which comes with the scale is easy enough to source when you need to replace. You can even consider looking at rechargeable battery option.
Mains: If you choose a mains only option you will be limited to where you can set up and use the scale, you will always need to be close to a source of power. Therefore a mains powered scale though very good it will restrict you to using only in the home.
Battery and mains: The dual option is always a nice choice because it doubles up your options for where you can use the scales. The price may well be higher but the investment would be worthwhile.
USB: This is a very good option, using a USB charger to recharge your system. Look for this feature when choosing a Macro diet measuring product.