Well this is all very confusing. You said "The standard adguard" (which is the one I am using and the one I am referring to) but you linked 2 different things. The first you linked is not "Adguard" but rather "Adguard: Content Blocker For samsung and yandex" (not standard adguard).
The second you linked is not even from the same company , and its called "Adguard VPN - Private Proxy" (Again , not the standard adguard).
The standard adguard can only be downloaded from their site. The certificate is needed in order to block ads on secure pages (https) otherwise it has no access to filter it's content. This is the only true solution for a device-wide ad blocking mechanism. Although it's setup as a VPN , no data is ever sent to adguard. It uses VPN functions to filter out the unwanted sites and blocks them , that's all.