I park outside but I don't think the shades have much of an effect on the final temperature reached in the cabin. But the roof and windshield shades help slow down the heating of the cabin, letting the A/C do less work when I'm out doing errands or keeping the cabin cool.
The roof shade really helps to make driving more comfortable. If you need it, you will know.
By coincidence I use the same windshield shade as Sara J (I got mine first):
Same here. Many things don't even fit with the rubber inserts. Glad to hear you got great customer service from Abstract Ocean.