It’s a great deal. For one-tenth of our defence budget and no regular UK troops Ukraine de-fangs our main military threat and speedruns our learning on drone and electronic warfare. We send them mostly older munitions, and it’s part financed by seized Russian assets.
Obviously, a weakened Russia is also a danger to us.
How you count that depends on whether you think Russian aggression was inevitable anyway. Looking at how active Russia had been with assassinations on UK soil and spying on assets, I tend to think that it was.