How much cancer risk is there taking a telomerase activator?

Likely good sized.: This helps to immortalize cell lines, and telomerase activity has been observed in roughly 90% of tumors, so it is likely to increase the risk of cancer considerably, also since this makes mutation of chromosomes much more possible. This also upregulates the role of 70 genes responsible for tumor growth and spread throughout the body, and the activation of glycolysis, so the cells can use sugar.

Dubious treatment: Don't spend too much money on what is at best an unproven anti-aging remedy. There have been a sad succession of failures and cynical frauds ever since telomere shortening in aging was figured out about 25 years ago.