uhh, my design decision to make the case modular had no bearing on my choice of Sliger over Protocase. That decision was actually made pretty early on when James pointed me in Sliger's direction. And that decision was made purely on the basis of cost and equipment—which pretty much also determines the cost.
You see, when I sent the most recent modular design to Sliger and Protocase for quoting, Protocase wanted something around $800 just to make one case (and that was after negotiation), while Sliger told me they could make two cases, maybe even three, for $500; take into consideration the progressive unit pricing discount of ordering in volume, and that's where we arrive at me being able to price the case at $150 today, of which I am very proud of.
This massive price disparity between the two manufacturers is largely due to equipment. Sliger has a combo CNC punch+laser while Protocase only has a laser (and some other machines too, just no CNC punch) to cut through sheet metal. Sliger's CNC punch+laser can punch and cut out repeated patterns, like the staggered slots all around my case, very very quickly. The laser only engages to cut paths and shapes that the punch tooling cannot. Protocase's laser, in comparison to a punch, moves relatively slowly, cutting and going along the dozens of meters of path length in order to cut out all the shapes in the flat pattern of the case, while also using more energy during all that time.
When you're getting something manufactured like this, it's not so much the material you're paying for, it's the time.
It was nice to be able to have the case production quality of both Sliger and Protocase as known quantities through James' various cases and Linus' (LinusTechTips) projects, so I had confidence in ordering from either of them. It all just came down to price. I didn't get my cases from Protocase, but what I did get from them was a whole lot of advice and knowledge about what can and cannot be done with sheet metal - and that is something I am very thankful for.
And that brings me to your second question.
To submit my design and get a quote from Sliger, I had to email Kahlin himself. He usually responded back the same day or the day after. Although there was a time where weeks went by before I got another response. This was because Sliger also has other orders to fulfill that may require much of their resources. It was completely understandable though. I know that I'm a low priority when they're dealing with companies and organizations that are much bigger and more important than me. To offset this delay, Kahlin suggested that I make the engineering drawings myself, as that would speed up the process greatly. I didn't have a problem doing that, so I did.
To submit my design and get a quote from Protocase, all I had to do was upload the 3D model of my case to the quoting page on their site and within a day or so, I was assigned a person who would take care of me and my project. They responded quickly, always emailing me back the same day or the next, happy to answer any dumb questions I may have had or talk to their engineers to let me know if there were any errors in my design. Very handhold-y, which is nice. But you know, as I said before, once Protocase quoted me their price, I knew I was going to go with Sliger instead. So to avoid wasting Kahlin's time, what I did was basically pinball between the two. I would email Protocase, asking stuff like what would be more cost effective, etc., then I would take that advice and make changes to my design and then prepare a new set of engineering drawings to send to Kahlin.
People should go to Protocase if they need more help in designing their case or need a case made super quick. People should go to Sliger if they're more experienced and are okay with waiting longer at the benefit of saving a whole lot of money.
I went with Sliger and had to wait a while, but in the end, I couldn't be happier. The wait was well worth it. Unboxing and seeing those parts exactly how I designed them is something, a feeling that is indescribable. It's like seeing your child be born - not that I know what that's like (I'm only 19), but that's how I imagine it to be.
Hopefully this short essay answers your questions.
