I just went over to Amazon and entered "olive oil sprayer" in the search box. There are ninety reviews ranging from "hate it" to "couldn't live without it". It sounds like following the instructions is imperative (imagine that!). Right now they are selling the "Misto" for $9.99 with free shipping - but - you have to spend $25 to get free shipping - Amazon's usual ploy to get me to buy more.
A reviewer mentions that she has refilled one of those liquid butter replacement sprayers with oil and that it works.
Some reviewers point out that the spray is not as even and the usage is not as convenient as using PAM, but they feel like the trade off of avoiding the additives in the commercial spray is worth it. Like many things, the old fashioned or homemade way of doing a task is not always the most convenient.
My interpretation of the reviews is that the sprayer is good for spraying your salad or veggies prior to grilling. It is not so good for spraying pans for baking because the sprayer needs to be pumped up repeatedly. Someone says it would be easier to wipe an oiled paper towel around the baking pan.