I don't own a lot of multi pens. Two, to be exact, and they're both different versions of the same pen: the Pilot Hi-Tec-C Coleto. To me, the multi pen evokes images of those chunky Bic multi pens they used to sell at the grocery store (or hey, maybe they still do), which would work for about a day before they crapped out. So I ignored multi pens for many years.
As the story usually goes, of course, I started listening to the Pen Addict Podcast and learned about the joys of the Pilot Hi-Tec-C. The Hi-Tec-C is my go-to ultra fine-point gel pen, but I often color-code my notes and there are certain times, like when I'm traveling, where it's inconvenient to carry around a fistful of gel pens in different colors or multiple fountain pens loaded with different inks. That's where the multi pen comes into play.
What I like about the multi pen is that it is completely customizable. My personal favorite is my Coleto Lumio, a higher-end model that comes in matte black. I have it kitted out with a .5mm mechanical pencil and .4mm blue-black, orange, and purple refills. For situations where I don't want to carry multiple pens on me, it's a complete solution.
If you're interested in dipping your toes into the world of multi pens, the Coleto is a great place to start. Amazon is selling the Black Clear Plastic body with a 10-refill starter kit, Prime shipping included. The Coleto Lumio is more expensive and harder to find, but is a very professional and nice-looking matte-black pen. (Other colors are available, too.) One of the great things about multi pens is that unless you are going really high-end, like certain models of the the Zebra Sharbo X or the Lamy 2000 multi pen, you're probably not going to spend more than $30, and often much, much less. At least not on the pen body itself.
Where multi pens eventually will get you is on the refills. The Coleto is far from the worst on this point: you can buy the refills in bulk to get the price down to about $1 apiece, and they last for a reasonably long period of time if you use them for moderately intense writing tasks like jotting down ideas in your Field Notes. However, if you're using a pen like the Zebra Sharbo X that takes smaller D1 refills, you will burn through the refills like there's no tomorrow, especially if you write a lot. You can offset the cost by avoiding D1 gel refills and moving to a hybrid ballpoint-gel ink like the Uniball Jetstream version, which last a good bit longer.
The Hi-Tec-C Coleto refills come in .3mm, .4mm, and .5mm sizes. As I mentioned, you can buy bulk color assortments until you figure out which particular colors you like, then stock up individually. For buying individual refills, JetPens and Kinokuniya both seem to have better pricing than Amazon, but I guess it depends on how many you buy and the cost of shipping.
DISCLAIMER: I purchased the pens featured in this review with my own funds, for my own collection. This post contains affiliate links. Any Amazon prices and availability is subject to change, and only current as of the time of publication of this review.