Rollerball Refill questions

This is probably a dumb question, but i promise i wont ask it again.
I recently purchased a couple really nice turned rollerball pens. Unfortunately the ink is out and i need to replace. I opened them up and they have schmidt 888. When i looked on Amazon there are different 888. My question is can i buy any of them, or are they specific to fit of pen? Are there high quality and low quality refills? I saw MontBlanc had refills, will they fit? Id appreciate any info you guys could pass on. I caught the bug, and i just want to know what im doing. Thanks

Not a dumb question. The number of refill options out there can be baffling. Any of the Schmidt 888 rollerball refills should be the same length and thickness, the difference should only be in the color of ink and whether it's a fine or medium point. And the point shouldn't keep it from fitting even if you had, say, a fine and replaced it with a medium.

The Montblanc refills might be a bit longer than some. I put one in a Pilot pen by trimming down the plastic end cap to make it shorter, but the quality of the refill compared to the much cheaper Pilot ones wouldn't justify buying one again. Don't know how they compare to the Schmidts.

Are Schmidt considered High Quality? googling this stuff does not produce anything helpful...lol

Schmidt inks are not bad at all, of you like them thats all that matters, im not familiar with them enough to know if they are standard sized or not which would open up a lot of possibilities

I mostly use fountain pens these days, but I think Schmidt is considered one of the better brands for rollerballs and ballpoints. I've used different sizes of their refills in different pens, and they worked well.

They claim (just taking this from Amazon) that their 888 refill will fit "98% of rollerballs that take a standard size refill". Putting that in reverse, there should be other "standard size" refills that will fit your pens, but I have no idea at all which to recommend. Maybe the pen maker can help?