hashstack reviews
I have read Hashstack being mentioned on a lot of threads here as an option for distributed cracking. The product seems very well put together. I was wondering if anyone has used is and has any experience with it. Also, if anyone has a link to a review, that would be helpful. epixoip, I know this is your tool and would like to hear from others about it. I have also reviewed hashtopus. Not saying it is any less or more than hashstack, just interested in user reviews of this particular tool. I read the rules for the forum and didn't seem like this was a forbidden topic. If it is, I understand. Thanks.
On a humorous note, GTX 970s might be available so cheaply soon that anyone can build a cluster of them for the price of one GTX 980.
I'll of course stay out of this conversation as much as I can since I am naturally biased, but I will say I'm not sure how many Hashstack users read these forums.

I know that some of our customers do read these forums periodically, but I'm not sure how many of them actually have an account & post.

EvilMog, rurapenthe, and m3g9tr0n from Team Hashcat use it regularly, but I don't think they read these forums often. net125mp is planning to write a review for his blog, but I'm not sure he's completed that yet. atom and magnum do participate on these forums and have been provided a copy, but I'm not sure either of them have really had the time to look at it yet.

So while I am interested in seeing what people have to say, I'm not sure this thread will receive much of a response.
I have been using Hashstack since December 2014, having moved to it from Hashtopus.

My setup is as follows:
4 compute nodes with 2 x 290X or 7970 (mixed).
1 controller node

The thing to remember about Hashstack is that it is geared for enterprise systems and the associated hardware that will be running it.
Therefore it is not a quick-fix for under-spec hardware, neither will it suddenly make your GPU's faster.

What it WILL do, is give you a professional platform for distributed hash cracking along with what has to be described as the easiest installation and roll-out method out of any tool you're going to find. Everything is done for you from a back-end configuration which takes the pain out of fiddling with AMD (in my case) drivers and configurations until you want to cry.
You are left with a user-friendly, functional and efficient web platform for managing your "attacks", sorting lists, how you use them, and of course uploading and managing cracking jobs. The exposure of API's make building on the foundation a simple process allowing you to extend it as much as you want. For example I have a python script that sends me any errors, or completed jobs/cracks to my Pebble.

I'll summarise my experience with Hashstack below;

Easy Installation (you really cannot go wrong unless you have never used Linux)
Intuitive and Functional Web Portal
Easy-to-Integrate API
Absolutely horizontally scalable of note, add new compute nodes in minutes.
Excellent built-in error handling and recovery of stopped/rebooted systems.
Wide use of log files for easy debugging.
Excellent Manual if needed and of course support.

This is not a toy! It IS hardware intensive and needs power.
Requires SSD's and healthy amounts of RAM in the control node.
Will need more RAM in compute nodes than a vanilla cli hashcat user. (although you shouldn't have too little anyway)
As it exposes a web interface you need to be sure your security is setup properly with regards to internet-access, passwords used and local ssh access etc. Remember to physically secure your machines if you will have sensitive data on them or run full-disk encryption on all machines (do not even try this if you don't have SSD's throughout and sufficient CPU power for the enc/de/cryption)

Thats my review of it, I trust it will help anyone using it. I am in no way affiliated to the product incase you're wondering, but it cannot be faulted as being what is probably the ONLY professional, highly-efficient and scalable distributed environment for hash cracking I have seen. And I've seen a lot.

PS - Some may say but there's other products out there. Yes there are, my point is some do a few things really well, Hashstack does a LOT of things really well.