I have been using this service, PIA for short, for nearly 5 years. Excellent customer service; they have helped me diagnose several DNS and ISP issues that weren't even their fault. 5 simultaneous connections allowed, software clients supported on Windows, Mac, Linux, Android, iOS. Servers all over the world; absolutely no logging of activity, so truly anonymous. You can even pay using VISA gift cards and popular store gift cards for complete anonymous purchase. I have paid using a Starbucks and Target gift cards, as well as pre-paid Visa gift cards purchased at the drugstore (Vanilla brand at Walgreens works fine).
Unlike Viscosity, which isn't even a service, only the VPN software, kill switch function and DNS leak protection built right in. Viscosity requires you to type in your own scripting commands for these functions. Viscosity also requires separate license purchase for Windows and Mac, and you have to manually create a separate connection definition for EVERY different server; plus you still have to find a service.
For a few extra dollars PIA gives you the service AND the software client. @Psychiatry mentioned below that he thought not being able to select a specific city was a weakness. and he is entitled to his opinion. IMO, I don't see that as a weakness. It is logical to assume the servers within a region utilize load balancing to ensure optimal bandwidth; that sometimes has to spread out over a region, not confined to one city, especially if users were specifically selecting a certain city at peak times. Also, the algorithms PIA uses attempt to find the best balance between available bandwidth on their end, and closest geographically from the PIA server to your ISP server, which isn't always near where you live, in fact, if you don't live in a major metro areas, probably is not where you live.
For example, people living in Los Angeles might assume their best connection will always be with a Los Angeles based PIA server, if they were allowed to select the city. Based on population alone, the Los Angeles PIA servers would quickly be saturated, and then customers would complain they wouldn't be getting the full speed they expect.. Then if PIA tried to move you off to a different city, like say San Francisco, it gets messy because you don't know if the customer will still complain about be switched over, so it's potentially a lose/lose scenario. They get either get complaints because customer was moved off of a city specified, or if they don't, customer complains they aren't getting full speed, (because the city is overloaded).
Consider, even though you may LIVE in LA for example, if you use a nationwide ISP like a Suddenlink or AT&T, the actual physical location of the ISP server that ultimately your connection goes out to the world from may be in a NOC (Network Operating Center) that is quite far from your physical location. So you might LIVE in Los Angeles for example, but your Time Warner ISP connection to the INternet may be out of a NOC in Silicon Valley, a major hub. After that, it's the routing time from your ISP's NOC in the Bay Area to the PIA server region you've selected that determines the shortest Internet route, not necessarily as the crow flies, in which case connecting to a PIA server in the Bay Area would be the most optimal, not Los Angeles. On the other hand if you connect at peak time and the Bay Area is saturated, PIA may route you in fact to Los Angeles, or Phoenix, etc.
You can't always trust what the IP GeoLocation says about your IP address either. Geo location may say your ISP IP is in Los Angeles, but your ISP is free to re-distribute IPs they are allocated throughout their service area. ISPs don't always update the GEo database. If the ISP gets a new customer in Seattle, that customer might get assigned an IP address that previously was geo listed in the Bay area. Same goes for PIA IP Addresses, PIA has contracts in all the regions with local service providers to carry the connection. PIA, i doubt actually physically owns the server they use, they outsource from farms, possibly even the same ISP you the customer might be using. So you can't always go by the geo info you get if you search on the IP address you get from PIA, again, other than by being assured it falls within a 'region'.
Anyway, that's hypothetical scenario, there are many variables used by PIA to determine connections, just my opinion. Lastly, I have a 50 mbit connection with my ISP. Almost always i get the full 50mbit logging into any PIA server, even overseas. If I don't get it, it usually means that region is peaking near bandwidth, and switching to another location will get me full speed. From my experience, PIA does not exercise ANY throttling at all.
Do your research, PIA is always at the top of reviews of VPN services.