Thanks for comments.
Izzie. Sigma 150-500 is OK but there are drawbacks with any affordable large zoom!
Heavy and somewhat cumbersome to use, particularly handheld. Autofocus is rather slow. Works best in the F8 to F11 range so it tends to be a good light lens.
But it gets you to 500 mm relatively inexpensively and has a handy size range. Stabilisation works quite well, but still best to use at 1/500 or faster for handheld shots.
Tamron have produced a 150-600 lens which has good reviews. Also, Sigma have updated their lens with a 150-600 and this seems to have even better reports. But( there is always a but somewhere
) it is more expensive and is heavy (possibly that means well constructed). If I was purchasing another long zoom I would certainly get the new 150-600 Sigma.