Web wallets present unique security challenges and are not recommend. Any cryptocurrency exchange that supports SiaPrime will give you SiaPrime addresses and allow you to send and receive SiaPrime. This is not a “true” web wallet in the sense that the exchange controls the private key and thus ultimately controls your SiaPrime. So as a matter of good practice, of course, the suggestion is only send what you need to, to an exchange and keep the rest in your wallet.
Our primary customers will not be exposed to a wallet or need to purchase and hold cryptocurrency as this will happen underneath the hood though we will develop mobile apps to access our storage product. For cryptocurrency investors and speculators, a version of the ledger device is available for Sia and may be ported to SiaPrime if there is enough demand.