Why would you invest in these? Far better returns for relatively similar level risk levels elsewhere.

Mine have been maxed out for year or two.
Never won anything of note, usually 25-50 per month. Still waiting on that bigger cheque!
I forgot the average % payout over a year period, but seems reasonable.
Premium Bonds
If you live outside the UK, you should check whether local regulations permit you to hold Premium Bonds. For example, the US has strict gaming and lottery laws which mean that it may not be possible or practical to hold Premium Bonds while in the US.
I invested three months ago and won £50 this month.