You asked
Is the tamron 70 300mm f 4 5 6 3 di iii rxd worth it?
Here is what the site says about that.
From Tamron 70-300mm f/4.5-6.3 Di III RXD: Tamron 70-300mm f/4.5-6.3 Di III RXD: A zoom lens by Tamron for Full frame cameras, 70-300mm f/4.5-6.3. A light, inexpensive telephoto zoom that relies on in-body stabilisation. Specs - Maker: Tamron - Focal length: 70-300mm (zoom) - Maximum aperture: f/4.5-6.3 (it gets darker as you zoom in) - Made for: Full frame sensors - Mounts: Sony E, Nikon Z - Stabilised: no - Autofocus: yes What it frames like - On full frame (Sony E, Nikon ...
From Sensor sizes: Is full frame worth it?: For low light, events, and portraits with very shallow depth of field, yes. For travel, street, wildlife on a budget, and most hobby photography, a good APS-C camera with good lenses is enough, and you'll carry it more. Lenses and light matter more than the last stop of sensor performance.
Quoted from this site's pages.