Great atmosphere and a lovely place to go to escape those long, cold winter days.
But be aware that the closer you are to the area of the garden with the piano, the further away from the food court's free Wi-Fi you are. And the more difficulty you will have finding an outlet.
Unfortunately the gardens are not a place where you would be comfortable working all day and that's not just because the chairs are uncomfortable. It's very easy to feel rushed at lunch time as there are a lot of business people vying for free tables to eat their lunches.
I would recommend visiting the gardens as soon as it opens at 9:30a.m. and staking out the coveted spot in one of the first seating sections by the escalator leading to the garden entrance. A small table of two by the wall features the only outlet in this section and a strong Wi-Fi signal. If you arrive later in the afternoon and can only find a spot by the washrooms, you might be lucky enough to get the one outlet there. However, you will not have a strong enough signal to connect to the Wi-Fi. I solved this problem by tethering my phone to my computer to use my 4G network but it sure eats up your data pretty fast!