I've had the big Sharp convection/microwave oven for more than ten years and have never had a problem with it.
I also have a Cadco convection oven 1/2 sheet pan size - they make a smaller 1/4 pan size. I've had this one for several years and did much of my baking in it - now do all of my baking in it because I got rid of my big oven (a gas commercial unit made by Blodgett) as it was just too big and I rarely used it.
If the temps are off in your regular oven you should get it calibrated. Built-in ovens and ovens in kitchen ranges should be calibrated at least every three years or oftener with heavy use.
If the sensors in the oven come in contact with a metal vessel they can be affected. Sometimes it is the control itself.
The more "automatic" an oven is, the more often it will need to be calibrated by a service technician. Otherwise the temps can be off as much as 100 degrees (F.) or 50 (C.), which can make from a disaster with most baking.
Sharp with a loaf of bread pudding:
And grilling some steaks.
Baking in the Cadco:
With an 11 inch skillet in the Cadco:
In the U.S. Cadco ovens are sold as "commercial" ovens but I know a lot of people who have them as secondary units because they can be moved around - I used to have mine on a rolling cart or "kitchen island" but now it has a permanent location.
It is very heavy, compared to a microwave oven, I can't budge it.