These are names given by some manufacturers for the combination settings that include a small amount of microwave energy along with convection heat. Low-mix usually includes 10% microwave energy and High-mix includes 30% microwave energy. Some manufacturers refer to these combinations as Bake for the low-mix and Roast for the high-mix. Some ovens have two combinations and some have only one. If your oven has only one combination, it is probably the high-mix. These combinations will usually reduce baking times to about half.
It is best to clean the oven with soapy water each time it is used. For cooked-on food, microwave a cup of water with a few drops of dish detergent for 5 to 6 minutes to get the oven very steamy. Let it stand about 5 minutes. Then, for light soil, a smooth-top range cleaner or stainless cleaner along with a mesh or nylon scrubber works quite well. For cooked on spots, Dawn® dishwashing detergent has a product called "Power Dissolver®" that removes cooked on grease. Several people have reported back on how well it has done. You spray it on or dab it on around area with holes and let it stand 20 to 30 minutes and then wipe it off. It may be necessary to repeat the application. Be sure to have plenty of ventilation and wear gloves with this product. Look for it in the dishwashing detergent area of supermarkets. I have not seen it in all stores, but it is available in some.
I never spray any non-stick baking dishes as it tends to destroy the non-stick finish. Good quality silicone should be non-stick and will perform best without any treatment. Occasionally for eggs or muffins that will be removed when warm, I lightly oil the bottom of a muffin cup, but for other things just allow the food to cool (the longer the better) and then it will remove from the dish. Several people have reported that their silicone became tacky after spraying with a non-stick spray. Silicone is dishwasher safe, but it may diminish the non-stick qualities. Dishwasher detergents often remove the light film that helps non-stick finishes release food. With muffin cups it may be helpful to lightly oil the cups the first time they are used since some muffins are fragile when warm and are more difficult to remove from the cups. The individual fluted cups do not require this since the sides pull down, making it easy to remove even very hot muffins.
Most ranges are on 220 volts of power and appliances used in the RV are on 110 power. So, the microwave-convection oven uses 110 volts of power and will be somewhat slower than the convection in a range. However, the microwave-convection has the option of cooking with a combination of convection plus a little microwave energy which speeds the cooking considerably and will usually reduce cooking time to almost half of the original. With a range convection oven, it is usually desirable to reduce the temperature 25 degrees and probably reduce the time by about 10%. With the microwave-convection oven, it is often best to not reduce the temperature and the time will probably not be significantly shorter. When using the high or low mix settings where microwave energy is introduced, temperatures can remain the same, but timings will be about half the original time. Both ovens circulate the air and in some of the larger microwave-convection ovens, it is possible to cook on two levels with equal browning on each.