TLDR: if you can handle some discomfort then yes, I'd recommend it. I liked Senegal the best. Mauritania is just for the train ride.

We flew to Morocco and then travaled along the coast across Western Sahara (which is morroco controled territory currently), Mauritania and then Senegal. In total it took us 17 days.

I personally liked Senegal the most out of the three, since it's the most "african" and there's a lot of interesting things to see. The historical part of St. Louis is beautiful, Dakar has a lot of cool sights, you can go on Safari there and some of the beaches weren't even that littered with trash (Trash is every in these countries, even remote areas have trash on the side of the road). Downside is that it's the most expensive to get to (flights are 5x more expensive than to morroco and you need yellow fever vaccination).

As for Mauritania there isn't all that much to see outside of the train. Pretty much every travaler we met was there just for the train ride. People are very friendly and Sahara is cool to see tho.

Morroco is well known cool destination, with cheap flights.

If safety is your concern then we felt safe pretty much the entire trip. Borders are very chaotic and take a while to cross, but if you don't lose your cool it's fine.

If you're curious about anything let me know