PIA (Private Internet Access), NordVPN, just to name a few. Do a little Google research, you will find many reviews and comparisons of VPN providers and the factors you should consider. For example, are activity logs kept? Can you purchase and pay anonymously, how many servers? What countries are the servers located in? Bandwidth? What country is the company headquartered in (very important, as some countries require that logs are maintained of activity, and can be handed over to law enforcement). What i mean by logging is that a record is kept of every instance you use the service, what IPs/addresses you visited, the date, time, your location you accessed from, YOUR IP (the real one) you accessed from, cross referenced to the AppleID you used to purchase your subscription (with the AppleID, from that someone can then gain access to everything Apple knows about you, your purchase history, payment info, the iTunes music, blogs, podcasts you listen too).
Read the privacy policy
https://www.keepsolid.com/privacy-policy
This company stores data for up to seven years, they do not explicitly say that they don't log or do log, which by omission is important to note, and they reserve the right to share your personal data with 3rd party, including law enforcement.
Does this make it a bad choice? That's up to you as the consumer, as to what level of security, privacy and anonymity you want (isn't that why you use a VPN. by the way?) but at least make informed decisions..Personally, and this is just my opinion, the fact that the client has to be downloaded via Mac Store is to me already a reason why I wouldn't use it, not because I'm against the Mac Store, but specifically in the case of VPN software where I want true anonymity, I don't want a record of my purchase , especially tied to my AppleID. By comparison, a service like PIA can be purchased using GIFT CARDS, including vanilla Visa and Mastercard Gift cards as well as branded cards like Amzn, Starbucks, Walmart etc. You can buy these cards with cash at any drug store, use it to purchase the service, this means ZERO paper trail of purchase of the service. PIA keeps NO LOGS.
Here's an excellent OBJECTIVE review by PCMag of many of the most popular VPN services; you will learn alot just by reading and udnerstanding the criteria PC Mag used to rate them.
https://www.pcmag.com/article2/0,2817,2403388,00.asp
and don't be confused when it says 'for Windows'. VPN services are not restricted by platform, and nearly all have Mac client software, and in any event you can configure VPN connection directly in MacOS and Windows without a vendor client app if need be.