Spencer waved are annual - easy way to tell after they have flowered is if they are perfumed or not - annuals are, perrennials are not. Any just labelled 'sweet peas' are going to be annuals, the others cost more usually. No, sweet peas are not difficult to remove, just pull them off their supports when they either get too moldy for you to bear, or actually dry up and die off, the roots are small and pull out easily. Sometimes they will seed around a little bit, which can be fun to find a seet pea where you least expect it. They grow quite happily over shrubs and along the ground, they don't always have to go up supports. Spencer are just a type of sweet pea with particularly wavy edged petals - usually sweetly perfumed as well, though some colours seem to have more perfume than others. The most sweetly perfumed are the smaller ones such as the original cuprani, but are not as striking as the newer hybrids such as spencer. Much will depend upon what you are growing with them of course, they do better on their own as the tendrils can twist about other plants and probably be a minor problem, but it is not one I have come across.