The dew cap is designed specifically for Vixen's 200 mm aperture optics and prevents fogging of your optics due to humidity and protects the telescope from stray light
Dew is often a real problem on clear nights. After just a few hours, the optics start to fog up, making observation or photography impossible. A good dew cap reduces the risk of fogging and thus extends the observation time.
The spirit level on the Seestar is built into the centre of the tripod, directly under the tripod head. This is impractical, as the Seestar is only screwed on afterwards. When screwing it in, it is very easy to misalign the balancing.