In this case, I think the extension (Membership Control by OSE) is excellent and well worth paying for. The extension itself does exactly what it says, which is great. However, what I believe separates it from other extensions is the support received. I needed some customisation of the extension and Helix did a fantastic job in turning it around very quickly. Having been let down by some developers in the past, this experience was a refreshing change.
Overall, I would say the extension + support is nothing short of outstanding so thank you!