I have gotten the vast majority of my channels from LN+. It's a great way to get matching inbound liquidity for your outbound. The quality of the peers can vary wildly though. Some will not honor the commitment they made to keep the channel open for X months and close channels early. I had one guy close our channel literally the day we opened it and did not respond to inquiries as to why. I've ended up in swaps with people that only have a few channels and never grow. Sometimes I get connected with nodes with terrible uptime.

What I'm trying to say is it's a crapshoot. I wouldn't even consider it a marketplace, because that implies you get to shop around and pick your product. You either just join a swap offer or make your own, and whoever you match with you are expected to open channels and honor the time commitment. You can restrict the swap to nodes with X amount of channels and X node capacity at least. As you get bigger and qualify for swaps with larger nodes the quality of peers should increase.

Overall I found it very useful for diving into LN and getting a feel for things. After I got myself established in the network it made more sense to be more targeted in how I open channels. Using analytics like LNDg or https://lnnodeinsight.com/ gave me suggestions on opening more productive channels and filling a need within the network.

As for Magma, I have sold one channel there and it has had zero activity. I get the feeling that Magma is for larger operators who can provide really well connected liquidity sources, and the customers are going to be merchants who really need and can use incoming liquidity. It's probably not great for a smaller hobbyist. I might be wrong though, my experience is limited.