Makarovs are great guns - very reliable and very accurate. I find its an enjoyable gun to shoot as well due to the fact that it is pretty light recoiling. The Bulgarians are the most common and aren't quite as well finished as E. Germans or Russians but are still very good. For a shooter you can't go wrong with a Bulgarian.
The 9x18 is similar to a hot .380 but does not have a great selection of defensive ammo in the Golden Saber, Gold Dot, PDX1 type loadings. That said, there are HP loadings from companies like Wolf etc. I tend to carry FMJs in my 9x18 weapons in a preference for penetration.
Makarovs typically fit well in Walther PPK marked holsters which makes it relatively easy to find a good holster.
If you prefer .380, there are barrels available (threaded and non threaded) and it is a pretty easy conversion. I have a .380 threaded barrel on my Makarov and it works well (though note that if you intend to suppress it, you may run into issues like excessive pressure and premature wear, even with heavy springs. It is still a very cool suppressor host though!).
As far as downsides for carry, it is relatively heavy and large for what it is. Sights on the Makarov are small and not easy to see, but white paint on the sights helps a lot. There used to be a conversion to put Meprolight sights on the gun, but I'm not sure if it is still available. And for the final point, a S&W Shied is similar in size, capacity, and price (if you find it on sale) but is in 9x19, has an American style mag release, and larger sights that can easily be replaced with night sights.
For a purely logocal "I need a smaller carry gun" type of thing, a Shied is probably a better choice. However, a Makarov is an excellent gun and would be fine for carry. For $300 you're getting a lot of gun with the Makarov, and there's certainly more history with a Makarov than a Shied, which for me makes it more fun to shoot.
Finally, be careful with Makarovs, they have a tendency to multiply. Just writing this post has me thinking that I really need a Makarov in the original 9x18 as opposed to my .380...