Fantastic lens at an affordable price for wildlife / birds. A prime, so fast focusing, a better lens than the 100-400mm because that's abit soft at 400mm. Don't knock the lens because it doesn't have IS, it still a great lens.
Alternatives are 300mm f4 (with and without a 1.4x TC) or the 100-400mm from canon or the low budget zooms from sigma, probably the best of the crop being the 50-500mm, although f6.3, so issues with shutter speeds and apertures due to light conditions.
Unfortunately the next step up is a big one financially with the main primes.