There are two parts to this answer.
First, let's talk about the core service. I believe Motley Fool is legit. I've been using their services on and off for almost six years. I started using them at a time when they were still sending PDF research reports and they always had some great insights. I've tested Jim Cramer's premium service as well (Action Alerts Plus) and I liked Motley Fool a lot better. Contrary to their marketing, the reports are actually well-researched and less hyped. They explain their picks and detail and warn of any risks that come with the stock pick. If you want more information on the service itself, this review does a good job of breaking it all down.
Second, let's talk about the marketing and upsells. In recent years, Motley Fool has been running some aggressive marketing campaigns. I'm pretty sure everyone has seen the "triple down" type campaigns. I'm not sure why the company went in this direction because it dilutes the professionalism of their brand but, personally, I just look past it. If you're going to buy into hype, you won't do well in investing - whether that's through Motley Fool, another service, or your own research.
Motley Fool's core offering is the Stock Advisor program and that's really all you need. It's priced at $99/year which is affordable and if you combine their picks with your own due diligence, the subscription can pay for itself. Don't get sucked into the hype of the special reports. Obviously, the company wants to upsell you, but the Stock Advisor program is the main service and it has a proven track record. As a member, you can see a history of all of the picks the company has ever made (losers and winners) dating back to the inception of the program. You really only need a few good stock picks to do well, so don't get caught up in the hype of "insider tips" or industries set for "explosive growth."
In the past few years, it's been very easy to make money following basic investment advice, such as the recommendations made by Motley Fool. Think about the FAANG stocks that have been a hot topic. If a company made a buy alert at ANY time between 2016-2018 it would have been a killer call. The market was hot and a lot of the most "obvious" companies reaped the rewards. The market environment is changing a bit now but Motley Fool has been around for over two decades.
The last thing to keep in mind is that a stock pick service helps you generate ideas but you still need to do your own research and control your own risk. "Buy and hold" strategies without regard for cutting losses may work well in the long-term but they could have costly short-term consequences. Take the FAANG stocks I mentioned above, some of which Motley Fool made recommendations on. A buy between 2016-2018 would have yielded amazing returns but a buy at the end of 2018 would have resulted in a "loss" of ~40% by early 2019. Luckily, those stocks recovered but you never know what the future holds.