I know a guy who knows a guy who subscribes to TSP Tips, and the guy said he got a return of 25% in 2018. Heh I know a guy who knows a guy.
YTD returns for all TSP funds in 2018 were terrible. If that service had him move his money almost perfectly into the best performing fund every month then it could have worked but that's like picking a perfect NCAA bracket or something. If he did each month like 100%: C, G, S, I, S, S, C, S, I, G, C, F as those were the best funds each month, he'd have gotten like 30% and no losses. I guess it's "possible" but unlikely some app/service will predict that accurately.
Have you ever worked with a paid financial advisor who helps people with investing for a living?