It will feel like some one is pushing on your teeth. The brackets stick out a bit from your teeth making it feel like you have a full mouth of metal, big lips and your bracket may rub against your lips feeling again like a metal file.
While some breeds may be more suitable than others for a beginner rider, there are always exceptions to the rule. Quarter Horses often make great beginner horses because of their even temperament, but some can be quite hot or energetic for a beginner.
I don't think that there is such a thing as a kids horse, or bombproof horse, those are marketing terms, but the most gentle breeds are the Morgan, and the Tennessee Walking Horse hands down! Draft horses are very sweet,but a kid could never even get on one without help, they are just too huge.