I am not a professional detailer, but like Pugga, I also like to keep my truck clean & detail it at least once or twice a year. I have never bought boutique products & but for my needs, Meguiars
products have worked perfectly fine.
From all the video's I've watched trying to learn how to detail vehicles the professional way, I think any professional will answer you question by saying: Is there a difference between boutique & OTC products? Yes, but there is also a difference between boutique product ABC & boutique product XYZ.
What you are trying to achieve & what you are working with (vehicle paint & condition) will dictate what you should use.