I had one of the XL Panasonic ones. I actually loved it. It cooked chicken in half the time of my full sized oven, and the skin came out way crispier. I could some french fries (home made or frozen) and two chicken breasts in 27 minutes iirc, instead of 55 in the oven.
Just shy of 2 years, the thing packed up. Even though you can get the same model everywhere, the store I bought it from stopped stocking it, and tried placing it with the "new model" which was just the small one with the touchscreen the XL had. I told them I can't cook a whole meal in it and got my money back.
Later I got a sunbeam convection oven for 1/6th the price. Now I mostly just use it to dehydrate banana peels for my plants, but I did a kassler chop in it yesterday, and it came out much better than my George Foreman.
TL:DR; They are only worth the counter space if you want to save electricity and heat in the kitchen, save a bit of cooking times, and don't have to cook for more than one person in my opinion.