Just so you know, the WYZE app for iOS / Apple is 148.3 MB. I suggest you look at the Android App Store to see the size that version uses on the phone’s memory, but note that as you use the different options on the Watch (sleep tracker / steps monitor / etc) there will be a little more memory needed to store the data on your phone.
As for the price, you really can’t beat it and I’ve never seen an addition discount for shipping unless it’s a special promotion. The $19.99 price is the presale price, there is always the chance that the regular price could be more after the presale is over. Based on the functionality on the Watch compared to other brands you are already getting a deal. Hell, it’s cheaper than the WYZE Band when I bought that and you’re getting a much bigger screen than what the Band has.
I bought the WYZE Watch to see how the larger screen compares to my Apple Watch because it was only $20 (and cheaper than the band I got for my Apple Watch) - worst thing that could happen is that I end up giving it to my daughter