I have been using the RAP 4 upgrades for about a month. I choose them because of their low price. They seemed like pretty simple parts and RAP 4 usually produces quality products from what I've seen/read. I really have no desire for the high ROF that can be gained through these performance kits but figure that the all metal parts would be more durable and put up with any punishment I could give them.

I must admit that I first discovered cyclone upgrades on an ebay auction selling a tech t product. They had some really cool youtube videos demonstrating what the upgrade could do. I did some reading and price comparisons and found the RAP4 kit. I couldn't find many reviews on the kit but for half the price I figured I would give it a try.

The instructions provided by RAP4 for their upgrade were poor at best and I actually got all my information for installing and maintenance from the tech t site. :P

After installation:
The parts seem to functioning fine although I have had some breaks when I mess around with high ROF. (I can't say for sure that these where because of the upgrade kit or because of old paint and low temps)
I took it apart after the first time I used it. I was having cycling problems. (This again could have been because of the low temp and high ROF. My friend with a stock cyclone was having problems too. Both of us using CO2) When I took the cyclone apart I noticed the pins on the ratchet lever were grinding grooves into the cyclone housing and bottom cap. It seems like the pins that came with the kit were a bit too long. I filed then down pretty good and also loosened the bottom cap screws. The motion seems to be working much better now but I really need to use it more to decide if this kit is really improving performance.

Even though I haven't been able to test this upgrade fully I have noticed some differences in the 2 companies and their product.

RAP4:
I have read that their customer service is not so hot. (I have never spoken to them myself.)
Not many customer reviews on their product
Similar product but quality and fit seem to be less than tech t
Installation instructions provided for this product are very poor
1/2 the price of tech t

Tech T
Product Creator
User testimonials and reviews (seems to be a proven effective)
Stronger marketing and greater market share
Great installation instructions on website
Good customer service
High price

IMHO
$100+ is way too much to spend on something that will improve your cyclone. I went with the cheap option to check out what all the fuss was about and am happy that I will never have to worry about a ratchet break but I don't see the need to spend so much money on something I will probably never utilize in a game.
I would suggest to anyone looking into these cyclone upgrades that if you don't need to shoot over 15bps right away you should wait on this one. Soon enough we will have more user reviews on the less expensive products and tech t will have to drop their price a bit. I would have definitely went tech t if it were only $10-20 more. After I fully test my RAP4 upgrade I will be sure to post my results.