In this segment from Market Foolery, Mac Greer trots out the theme of "Yes, No, Maybe So" for Motley Fool analysts David Kretzmann and Matt Argersinger. Each Fool tells us about a trend they feel bullish on, one they feel bearish on, and one that has them on the fence.

Here, Kretzmann explains his bearish outlook for fitness trackers. And based on his reasoning, it's all the more tragic that Garmin (NASDAQ:GRMN) is making such a big push into the niche.

A full transcript follows the video.

This video was recorded on May 24, 2017.

Mac Greer: David, what are you saying no to?

David Kretzmann: I'm saying no to fitness trackers. I'll just say that this isn't saying no to wearable devices as a whole. But fitness trackers themselves, something you put on your wrist to track your sleep, your heart rate, your running speed, your distance and all of the, I think that's a future and not a product. It reminds me of Garmin 10 or 15 years ago, where you have these dedicated GPS systems, but lo and behold, it gets integrated into virtually every phone and device out there, and you don't need a separate GPS system. I think fitness trackers are just something that, they won't necessarily go away. I think that feature will be integrated into smartwatches or glasses or whatever wearable devices we have. But, between 2009 and 2015, U.S. navigation system sales dropped from $15.5 million to $10 million. Garmin's share price over the last 10 years is down 10%. And I think, you'll see something similar play out with Fitbit (NYSE:FIT), which, for 2017, they're guiding for the revenue to drop, they're back to losing money and burning cash. Since Apple (NASDAQ:AAPL) entered the smartwatch market, it still surprises me that people give the Apple Watch so much grief, because ever since Apple entered the market in 2015, it's never dropped below 50% market share. Right now it has 63% share of that smartwatch market.

Greer: But is that one of those stats where there were four watches sold and Apple sold two of them?

Kretzmann: No, you have a good amount of competitors now. You have Samsung, Fitbit has come out with a few different smartwatches. But ever since Apple entered the market, they've dominated it. And I think that goes back to my previous point, where, when you buy an Apple Watch, it's fitting into an existing ecosystem. And I think that's similar to GPS, where it's a key feature, but people aren't going to buy a product just for that feature.

Matt Argersinger: I love the point -- if you're an investor listening to this podcast, I think David just said some really smart things. Watch out for products and services that are merely features, that aren't part of an ecosystem, or a product that can do a lot of diverse and versatile things for you. There are a lot, you can look in business all the time, and see situations like that. Maybe there's a cyber security firm like FireEye, I'm throwing out just one that has underperformed lately, where maybe what they do is more features, it's not necessarily the one-stop solution for my cyber security. I'm just making one example here. But, those exist all the time. They key to investing is really finding those companies that are actually building the platforms and ecosystems that consumers are going to keep coming back to and that keep getting richer, whereas companies that just do one or two things really well tend to get gobbled up pretty fast.

Greer: And Apple has deep pockets. They don't have near as much riding on the smartwatch as Fitbit or a pure-play has.

Kretzmann: Yeah, Fitbit is really going back to the drawing board, and they're reinventing the company. They're saying, "We're a data company now, we're going to try to sell the data that our customers are tracking." To me, it's just not a very compelling vision for the company. I see them in a similar position to Garmin five or 10 years ago, where yeah, they did that one thing really well, and they were the leader in that market, but at some point, that feature will be in everything, it won't be differentiated anymore.

Argersinger: Right. Imagine if Kevin Plank at Under Armour 20 years ago said, "You know what? I'm just going to make the sweat wicking undershirts, that's all we're going to do. Under Armour is going to be the best in that." Well, it wouldn't have been long before NikeAdidas, or someone else did that or bought Under Armour. But, no, he said, "We're going to create a brand that does a lot of different things, that goes in a lot of different markets." And you can see where their success has been, doing that.