I own the Coleman Stove Top Oven, a Camp Chef Deluxe Oven, Camp Chef Professional Oven, and the Omnia.
There is a learning curve with all of these products, and some are dependent on your stove and some are limited by the product itself. If I was going to start from scratch I would go with the Omnia for light camping when I want the most minimalist setup while still want oven cooking. I would also go with the Camp Chef Professional Oven when I bring my trailer.
Coleman Stove Top, I've never been able to get consistent results with this, I'm sure if I stuck with it, I'd be able to figure it out and get the results I want, but it is limited in size and the folding capability doesn't make it the most stable of setups.
Camp Chef Deluxe Oven, great concept, poor execution, I was never able to get the Oven hot enough, nor stable enough in temperature to get .the results needed to fully cook something. I believe this is because the oven portion is underpowered. This product is now only kept at home for emergency situations.
Camp Chef Professional Oven, this version has upped the output for the Oven portion and has meet my expectations of great concept to great results. The biggest problem is the size and somewhat the weight, which is why I only use it when I bring my trailer where the size is not as big as a problem. This product also lives on my patio in my outdoor kitchen as I get great results and don't have to heat up my inside kitchen during the summer and bake on my patio. I love this product.
Omnia, probably the biggest learning curve, but once learned against your stove top and how the Omnia reacts to different temperatures and recipe setup, it is a great minimalist solution and always goes with me when I go camping. The other big plus to this is you can use it on your indoor/house stove top to really learn how to use it. In my opinion this is the best all-round solution in terms of price, size, performance, and weight. I do suggest getting using the silicone accessories, that make cleanup a breeze. Yes you have to get use to working in a ring and your recipes have to be altered to have ringed baked goods rather than square and round. The Omnia is the oven and the baking vessel all in one.