We stopped here on our way to stay at Hana for a few days to get a few groceries. Mana was recommended by posters on the Hawaii forums, which is why we stopped. Parking was a bit of a problem but we found some close to the store.
The store is very small and unique. Something like a funky, hippified Trader Joe's. My daughter is allergic to diary & she practically swooned over the non-dairy selections of cheese, yogurt, dressing, etc. Lots & lots of options that we have never seen in Northern Virginia. This is not to say that this is a totally vegan place - I was able to get regular yogurt & turkey lunch meat.
There is an emphasis on local produce. One real Hawaiian treat is apple bananas & Mana had plenty. They also have a small deli for food to go. Service was super friendly.
We had planned on visiting only once on our way to Hana, but there were so many daughter friendly options, we also visited on the way back.
Food is expensive but fair considering that Maui is in the middle of an ocean & it's a comparatively small store.