My 831 with the upgraded rear triangle is holding up fine with around 1300 miles of trails with jumps drops and janky rocks and roots, Turned out to be a great frame in the end, still love mine

Flex issues have been resolved with the new rear triangle , The only issue remaining is the fork crown clearance on the down tube. I had to run a 10mm spacer on top of the fork crown , I've hammered mine and it has held up well and rides great

When I first rode my 831 I found the rear suspension to have a bit of a dead or sluggish feeling , It would blow through the initial travel and just work in the mid and end stroke, I tried raising the air pressure which helped but it was harsh and I wasn't getting full travel , Looking on the Santa Cruz forums It seems they were having the same problems , Im running the same shock the Rock Shox super delux with a mid tune, A lot of them were having good results by fitting the Rock Shox Meg Neg so I fitted one to my shock and what a difference It now has a lively feeling , great mid range support, holds up well in high speed berms and g outs , popy and playfull , It takes a bit of time to set up and its not really suitable for heavy riders because of the increase in air pressure needed , Well worth doing if your running the delux or super delux shocks   

I have a Kacktus press fit installed with a little medium lock tight applied and its still going strong , I have the Zitto one for when the Kacktus bb fails but so far 600 plus miles and still going

I have both the JJ fix and the mod rear triangle , The jj fix was a big improvement and I rode it for a good few miles with drops jumps and ruff descents and it was fine
I got a good discount on the moded rear triangle so I went for it and it is slightly stiffer but not noticeable when riding, I have done 650 miles on the frame now with bike park days and mixed local trails , The frame has proved to be strong and handles really well especially on ruff descents, apart from re tightening the pivot point bolts a couple of times I have had no issues with it
I have had a lot of full suspension frames from Intense, foes, scott, giant, trek, yeti and Vitus a lot of them had issues some big some small I've had warranty claims that have dragged out for a year and some that were deemed void and I had to pay for the replacement parts to fix it,   so getting a modern carbon frame that builds into a great very capable bike for less than a $1000 is a good result even with a few teething problems   

I replaced all the bearings on mine when I fitted the new rear triangle and its been fine , The original bearings are low quality and some of them were already feeling notchy after only a few rides. I've now covered almost 300 miles of local trails and bike park trails without any issues.
I have converted to a mullet set up which i really like

Of course, feel free to contact me eddy@haidelibicycle.com

Its only the first frames that have the flex issue , The new frames with the upgraded rear triangle are great

After around 50 trail miles I have had to park the 831 , The movement of the bearings in the seat stays has become excessive so for fear of making the bearing housing oval or enlarged I've stopped riding it until JJJ's bolts are ready or the replacement rear triangle turns up.
The few miles I have done so far have been very impressive , Once the rear shock was set up the rear gives that endless travel feeling and the ride is fantastic , Its definitely more at home at speed and descending , Really stable over jumps and high speed corners but not so good in slow twisty single track where it feels a bit big and clumsy . I have fitted the Meg neg air chamber to the Rockshox super delux shock that I'm using and whilst it transforms the ride performance on the back it has made pedal bob worse when climbing so for long climbs I use the lock out
Just thought I would leave a quik   update on my impressions of the frame so far