When you sketch on an iPad or tablet, no subject has a clue they are the subject. All those glances their way are just you taking a break from your book or game. IPad sketching is much more discrete than art pad and pens. Given practice, finesse can be achieved. Right now, I'm at the comic illustration stage, but the more adept I get changing tools, noting the power of the colors and the art of blending with the palette knife, the more I think some serious paintings can be produced.
Right now, it's great for catching the moment. I did that first with this woman who also fidgeted--not because she knew I was drawing her, but because they had just arrived and was arranging her spot at the pool. Then, when she just couldn't settle down with her book and strode off towards the beach, I finished her off from memory.
Good enough. I have a feeling I should have left all supplies at home this trip. My creative cup is nearly depleted and needs a break. The iPad is about all I feel like doing.