I have a Wolf convection steam oven and love it. It's not plumbed, which you probably already know. It has occasionally run out of water while cooking but when that happens, the oven beeps, opens the door to the water reservoir automatically and displays a message to fill the tank. When I remember to check that the water tank is full before cooking, I haven't had a problem with it running out during use.

The $400 is definitely worth it, but the cost could go up dramatically higher if one had to add water/drain lines; especially if there is no basement underneath.

Thanks, everyone. This is for new construction, so hopefully, the charge for adding the water/drain lines won't be too much. It doesn't seem like there are any other downsides to the plumbed version besides cost.

Only other downside would be if something breaks or the line gets clogged. Could leak water a while until it gets noticed.

A Wolf rep told me that they decided against making a plumbed-in model, because their research showed that 90% of the problems with these models are plumbing-related. This may very well be marketing hype though.

Aside from that, mold can only grow on organic material, so there's no risk of mold growing in the tank.

After reading about sous vide cooking I wish mine were plumbed - a recipe I was reading you sous vide for 24 hours