I would say the main benefit that Sparrow has over Electrum is how easy it so connect to your own node and not rely on a third party. Electrum requires that you set up an Electrum server on top of your node first; Sparrow can just be pointed directly at your node. Sparrow also allows you to Whirlpool directly from your wallet, as well as supporting other privacy improvements such as PayNyms and Stonewall transactions, but this is probably irrelevant if you are just going to use it as a watch only wallet.