It's not a matter of "belief" or being a "purist" . It's a matter of knowledge, just plain ole common sense and practical >facts< of how things >actually< work. Beliefs are subjective and people can believe anything they want and more often than not beliefs are tainted by the individuals wanting to do something regarless of any pertinent facts or empirical evidence.
DE while apparently being an inert substance there are a few things that it will do that can affect how the MC works. One is that main workings of the MC is to give the digestive system a rest so the energy otherwise used for digestion is used by the system to cleanse and heal. DE being a solid will activate the peristaltic action in the GI tract to push it out and 2 being a non soluble fine powder and not having other solid matter to help push it out it can possibly cause a blockage and 3 since it also acts as a vermifuge to kill parasites this can cause the release of toxins from die off which could make it very unpleasant and if there is more die off than the system can handle, it can cause a herxheimer reaction and make one very nauseous and sick.
#2 sounds like a reasonable statement unless one considers the facts and mechanics of how things >actually< work and not blindly speculate on what Burroughs might have experimented with. The MC has proven effective as is for those 50 + years and it is certainly not the only way to cleanse so why try to reinvent the wheel? and in the vast majority of cases by folks that have not experienced the MC or have little to real knowledge of the interaction of these supplements when they can simply choose to cleanse the system in another way that includes supplements etc such as "Juice Feasting" ( http://files.meetup.com/577895/A%20JuiceFeaster%27s%20Handbook.pdf ) which I am currently doing and on day 36 of 90 and feeling amazing.
The Green Star is prolly one of the top 3 juicers out there. It's a twin gear auger juicer and supposedly it has some kinda magnetized voodo mojo in the augers that helps preserve the freshness of juices. It is not cheap though. The Breville is a centrifugal juicer. The plus is that they are fast but they don't do well with leafy greens or soft fruits and it will not do wheatgrass and some of the other neat things like make nut butters or delicious frappes with frozen fruits. It is also cheaper.
Outside of those 2 choices if on a tighter budget I recommend the Omega 2004 which is what I use cept the older 2002 version. It cost is less than half of the Green Star and it has 15 year guarantee. Mine is at least 10 years old. I had a part break recently after 10 years of regular use and all I had to do was email them a pix of the broken part and they replaced it free within 3 days of me contacting them. Omega also has brand new design that is called the Omega Vert 330HD and all the reviews on it are great. Search for it on "YouTube". Actually you can find demos/reviews of all these juicers on YouTube