Lots of questions here so I'll try to give my answers based on my experience in playing with both biscuit types and CAMO, as well as my customer feedback.

I'm now leaning towards preferring CAMO as a hidden fastener because I think it gives you the best stability possible out of all types of hidden fasteners. With CAMO, you are putting two screws into each joist at a 55-degree angle. With a biscuit system, only one screw. I also like the fact that if you do have problems with a board, you can remove the CAMO fastener and remove the board and replace. It's much harder to do with a clip system and even then you have to plug the replacement board on one end according their own instructions.

The gap is a little wider but I don't think you will be able to tell much of a difference with a 6" board. They have a 4" jig out now. How much airflow do you have under the deck? How high is it off the ground? These factors are important if you ware worried about cupping. Most cupping I've seen is due to no airflow underneath and the deck is low to the ground with a moisture imbalance. A thicker and narrower board helps prevent this, so 5/4 thickness would offer more stability than 4/4 if it works for your budget, but I've seen CAMO used numerous times on 1x6. The screw hole will ride a little higher on the eased edge of a 5/4 board but still very minimal aesthetic. You can see the screw holes if you re looking at them from an angle, but over the top they are barely noticable. Since Ipe is darker, especially if put a finish on it, I don't even think you'd notice them.

CAMO's stainless steel screws are 316 stainless (vs. 305) which is what you would want for a salt environment. They are more expensive, but if you do the math with CAMO vs. clip system, CAMO comes out less expensive and I think it's more secure.

Finally, PRE-DRILL your holes. Stainless Steel is soft and you will strip out more scews than you care to if you don't pre-drill...and let the screw do the work, don't push down on it. CAMO says you don't have to pre-drill but they do recommend that you do for hardwoods. I concur on this with my testing, especially when you are close to the end of the board. I was able to set the stainless screws without pre-drilling, but I stripped out or broke the head off of 1/3 of them and the boards cracked where I tried to fasten them at the ends. On my pre-drilling tests, they set perfectly.

Also, if you decide to go with the CAMO, get the PRO jigs since they have screw guides on both sides, making it easier to install without moving the jig. And get two jigs so you can properly space your boards, as well as a BoWrench to make sure they are snug when you are fastening. Start with the outside part of the board (pushing back inwards to your boards already laid), then fasten the inside edge to keep them snug.

I built a little 2x2 sample deck out of Garapa using the CAMO sytem that I can send you some pictures of if you want to see them.

If CAMO was available when I built my dad's Ipe deck, I would have used it (we face-screwed and plugged it).

Every person I have talked to who has used CAMO has loved it, even an installer I know that hates clip style hidden fasteners but now uses CAMO on every job. I've only had one installer say that he didn't like it, I think becuase he was pretty set in his ways and did't want to take the time to get used to it. So I recommend that you practice on some scrap pieces before you use it on your main boards.

I think CAMO just cut a deal with Lowe's so you may see them in the store soon. There are plenty of online retailers to buy from, so maybe buy one jig and a small 100pc package to play with them to see if you like it. If not, keep the jig packaging, clean it off and send it back. Minimal investment to test it out.

Sorry this is long but it's my .02. Hope this helps.