As always, it depends on use case and needs. For my use case (hot storage for vm disk and stateful kubernetes workloads) Truenas Scale doesn't require any tinkering. Just install it and configure the storage, networking, and shares. The latter of which is currently completely handled by a kubernetes operator. This is about equivalent effort to Synology but with a much less user friendly interface.

For more than a storage target, I wouldn't really recommend it. It does have "Apps" but the setup is semi-involved and does leak some of the implementation details. You can also run vms but the experience is much worse than a dedicated hypervisor.

So, I have both for different purposes. I wouldn't want to put my hot storage on Synology because the hardware is pretty expensive and gets really expensive to get the features I would need (10gb and likely more ram to support the workload) but it's pretty good for bulk storage and the app platform is fine for the supported things.

So, I'd say that a new Synology is probably best for you. I upgraded from a DS1513 to the the DS1821+ and the improvement is nice. I would recommend you get more bays than you need as it makes gradually increasing your storage smoother with SHR. If you use SHR, SHR-2 is the one to use as a failure during rebuild isn't exactly unlikely with similar drives. Since that requires a 4 drive minimum of a particular size to make the space usable, 5 drives is pretty limiting in terms of incrementally upgrading.