Very safe, for three reasons.
Firstly, the way it is legally set up – in addition to being issued by a large insurance company licensed and regulated in multiple jurisdictions, all customer assets are held in separate “segregated portfolios”, which means that your pension assets are held separately from company assets, and separately from other customers assets. This is not a company, group, or government pension plan which can have the terms and conditions changed by company directors or politicians. It’s yours, and yours alone.
Secondly, what it is invested into – 100% of the money you pay into your pension plan is invested into the S&P500 Index. This means your pension assets are highly diversified, giving you a piece of ownership in all of the largest 500 companies listed on USA stock exchanges (which includes many non-US companies as large companies are often listed on multiple stock exchanges), and a share in all of the dividends (profits paid to shareholders) that these 500 companies pay over the duration of your pension plan. The companies included in the S&P500 Index do sometimes change, because the value of companies change over time based on their performance and other factors, so companies breaking into the top 500 will replace companies falling out of the top 500. This means that neither you nor anyone else needs to manage the investment or make any decisions about what to invest in – it will automatically always be invested into the top 500 companies which comprise the S&P500 Index.
Thirdly, this pension plan has a minimum guaranteed value, as long as you stick to the plan. This means that even if the stock markets crash just before you reach the end of your chosen duration, you’re not going to lose any money, and in the case of the 15 & 20 year options you also have a guaranteed minimum profit. Whilst it is highly likely that you will not need the minimum guaranteed return because you can reasonably expect the value of your pension plan to be significantly more than the guaranteed minimum, it’s there just in case, so you can be sure of what you’ll have as a minimum, and therefore be able to plan accordingly and not worry about how Future You will survive financially in retirement.