If you want to save money, PS油 is ok. Because you can spray PS on hard plastic, one problem is you won't get gloss finsih using PS on hard plastic surface. Keep in mind just don't use TS on 透明車殼 and you will be ok.
PS on hard plastic is ok, PS paint is flexible and stick to surface even on hard plastic. 落雪 will only happen if you use TS on 透明車殼 or on any flexible material.