The app or the lack of it is not a problem. It’s very easy to start a storagenode on Synology also, without a dedicated app. Fewer things to go wrong. You can find reviews and comparitions for most models of Synology vs QNap, for the hardware part. For the software part, I prefer Synology because there is no thirdparty dev (except for the optional addons) and DSM seems more stable and secure than QNap. But, I don’t have any expirience with QNap. If you have questions about Synology installation, just check all my topics. I got answers from the community for all things that should arise.
One of them: