The idea of the Masterspool is pretty new, but as many things in the RepRap world, it evolved quite quickly and successfully. Basically, it’s about shipping filament without a spool using a very specific standardized size which allows users to put that ‘cartridge’ / ‘refill’ onto a 2-piece spool that they can either download from the internet or design themselves and print it. When the filament is completely used up, you won’t have a 200 - 300g plastic spool that you have to throw away but instead you will have that 2-piece Masterspool ready to be refilled!
As I said, this is all still in the beginning: Richard Horne (RichRap) came up with the idea only a few months ago, at the beginning of this year - MasterSpool - A proposed standard for 3D Printing filament supply without a spool. Still, multiple manufacturers liked the idea and have already implemented it, amongst which dasfilament is the most relevant to me as they’re a German company which is where I live and I’ve used their filament (on spools) for multiple years now.
Let’s talk about the ca$h: in the case of dasfilament, you don’t save a whole lot of money; you essentially get 50g more compared to an equally-priced 800g spool of filament (same material, color, ..). In my opinion it’s not a lot and I expected the refill to be even cheaper or include more material, but for me it’s totally fine as obviously all of aforementioned benefits still count. You might still want to check the difference in price between refill and spool for your specific reseller as it might really run you a lot cheaper. Also, prices are always subject to change and I have no idea about what dasfilament or any other company is planning for the future, so maybe when you read this, the discount will be larger.
One little hiccup for me - hence my expectations regarding price difference - was that the ‘suggested’ / ‘original’ STL file for the printed spool was always estimated at around 300g, even after tweaking infill and wall thickness settings in the slicer. 300 grams is a lot of filament and I’d need to buy 6 refills from dasfilament per each printed spool to at least break even! As a small side note: Once you put a refill onto any spool model, you can’t really take it back off, because you cut the zip ties, so using multiple refills with one spool is not really an option.
Fortunately, and essentially the reason for me to get refills instead of spools for the first time, was that dasfilament uploaded an alternative spool design on Thingiverse: Little MasterSpool which only required around 50g of filament to print! That’s great, because essentially you use the 50g of extra filament that you get on the refill to print the holder and every refill that you put onto it after that is giving you 50g ‘for free’.

Little Masterspool Refill from dasfilament Refill on the Little Masterspool With zip ties removed

My experience and recommendations

As I said, I printed the ‘Little Masterspool’ to save filament and that model itself was the only thing that gave me a few minor issues. The Masterspool ‘experience’ itself is very simple and works great, especially considering it’s around for such little time.
When my first refill was brand new, the arms of the ‘Little Masterspools’ were just a little bit too short to prevent the filament from falling off the edge, but that was resolved after the first 10 minutes of printing and after carefully aligning the spool holder with my bowden extruder so that it pulled in a straight line. Maybe on a direct extruder, this will be a little more difficult as the printhead with the extruder obviously moves on the X axis - in that case you can just use one of those ‘filament guide’ clips e.g. to put onto the top of a Prusa frame.
If you have a lot (300g worth) of ‘waste filament’ / rests from different spools, you can do what Joseph Casha (3DMN) did: Using Up ALL of your Filament In a Functional Way and use those rests for a multicolor-version of the original design: Masterspool v4, as it’s obviously purely functional.
Another alternative is to check the Little Masterspool Remixes page which is full of great alternatives to the Little Masterspool that still use little filament. For example, I would highly recommend to print any of the remixes that offers some sort of holes to put the the beginning of the refill into, because the original ‘Little Masterspool’ lacks it and I had to secure it with some tape to one of the 3 posts.
Also, the filament slipping off the edge at the beginning could maybe be prevented by using one of the ‘roller’ remixes.

Just as a little addition, Thomas Sanladerer also made a nice video about the Masterspool that I recommend watching: 3D printed filament spools!?.

In conclusion, I would definitely recommend the Masterspool! I’m glad that you can print your spool for very cheap and very quickly, because having to print a 300g piece would just be too expensive for the whole thing to make sense.
Every time I saw multiple empty spools sitting around on my desk, I thought ‘what a shame all of this is 1-time-use’. So the Masterspool is the ultimate solution to having 300g of ‘packaging’ produced, paying for it and its shipping and having to dispose it, harming the environment when we’re talking about a 800g ‘product’! The weight of such a spool is almost 30% of the spool+filament weight!

Check out the links, get your own Masterspool refills and feel free to design, remix and improve spool designs as well as share the word to get your favourite filament manufacturers to offer refills, too!