It depends upon how you want to use that second oven. The microwave/convection oven requires you to choose between a glass base or a metal base, depending upon which process you're using. If you envision using the Advantium (I presume the other alternatives are similar in this regard) for an oven frequently and you also use a microwave frequently, I think you would find changing these out irritating. If, instead, you will only use it infrequently as an oven and frequently as a microwave, then it's easy enough to use. My Advantium preheats in roughly 5 minutes. It cools down very fast and I have not had any problem using it as a microwave right after using it as an oven. (I'm using it now on the countertop during the temporary kitchen phase. A real godsend!) If you go this route, you want to have a convenient location for storing whichever base isn't being used at the time along with the rack that isn't used during microwaving.

For our current house (built in 2007), we installed a 220 Advantium and a Trivection oven. We've used the features of the Trivection oven a lot and would buy another one for the house we're building next year--except it's been discontinued. We never really learned how to use the Advantium fully so we've basically used the Advantium as a (very expensive) microwave. I like speed bake on the Trivection because I'm always in a hurry and short on time. I didn't take much advantage of the 3 cookie sheets at once functionality, though, even though I do bake in bulk. My original thought was to get another Trivection oven and a "standard" wall microwave. Obviously, that won't work now :-) What should I look into for our next house? I'm planning a single oven and a microwave (not a microwave drawer).

We have an oven/microwave combo (KitchenAid). If I could redo my kitchen I might do that part differently. I did not know when I designed my kitchen last year that microwave drawers were a thing. If I had known I might have chosen that with a built in oven instead. I do not dislike our oven/microwave however I do have concerns about the microwave breaking. The fan was actually broken when we installed it, and we had to get it repaired. So if something happens to it, I know we will have to pull the entire unit out to get it fixed which is more of a pain than just fixing a microwave. The other issue I have with it is that microwave is a little higher than I would like. We installed the unit 1.5" higher than they recommend (so I could have a 15" drawer below) and since I'm only 5'3" the microwave is a little bit high for me. Even installing it at suggested height would still leave it higher than the ideal. A drawer would be a nicer height most likely. I definitely like having a separate gas rangetop and built in oven. There are many reasons I want them separate, so a range was never an option for me. But I probably won't combine the oven and microwave again if I did another kitchen.

So, make a niche(s) with the proper electric service and size to have a built-in put in if you really need it to sell (but I bet you won't)--if you're planning to sell within three years, get the built-ins already, but otherwise, they're going to be just so many used appliances. If yours are truly ratty, you can buy new versions of each. If you WANT a speed oven, and intend to use it as such, that's another story. Go for it! Read through the manuals, etc. But I think you'll find that it's not at all the same thing as your Breville toaster oven. You can use the convection oven settings on a speed oven to perform some of the same functions, but it's a real oven, with limitations, not a toaster that tap dances. I sometimes use my speed oven the way others use a toaster oven--mainly for heating up frozen appetizers or reheating casseroles when other ovens are full, but my old (dead) toaster oven was beloved for making great toast, which a speed oven isn't, and not for other uses. I do zap sandwiches on MW mode, and once in awhile lightly defrost or melt, but if I used a microwave more, I wouldn't have such an expensive machine doing it. I agree with putting enough thought into a remodel that it won't limit resale, because you never know what the future will bring--thus make sure there's place for built-ins to be built into--but unless it's a flip, it should be designed for your own use and enjoyment, and you used the key words "heavily use" and "love".