Lots of people have heard of them. I would say everyone has heard of them, but with your question I guess that is not true.
Pros
Lots of deal flow. Some people depend on them for all their deal flow. If you have a deal to sell, they might buy it from you. If it is a real deal and title is good/clean I would expect them to close if they contract on it. My guess is they probably have a higher closing % than most other wholesalers you might sell to. Probably one of the longest lasting and highest volume wholesaler type organization in multiple cities. They've very good at what they do.
Cons
Do your own due diligence on ARV and rehab costs. KNOW your numbers, don't depend on other people to do that work for you. As with most wholesalers often ARVs will be way too high, and rehab costs way to low. Comps often cherry picked to support the values. Really good chances your spreads/profit will be less, especially if you are new.
Remember "off-market" is just a marketing term, and one many new investors get sucked into. All it might mean is that it is not on MLS (maybe). It is certainly being marketed. If there is a showing day/time don't be surprised to see 40 other investors there. Often you will be asked to make a decision within an hour and put up $5000 in earnest money that is non-refundable. People often say that "newbies" get sucked into the excitement and only buy from them once. However that might be true of any wholesaler and new investor. They motivated to buy, don't know their numbers, loose money on that deal and then get soured on the game and quit. Also don't get soured on MLS opportunities, as some of their deals get purchased off MLS and then recycled thru wholesale channels....so you could have done the same deal for less, maybe $5000 or more, but also buying off MLS and cutting out the middleman. Can't tell you how many of my investor clients call me saying they've gotten a "wholesale" "off market deal" that I sent them 2 weeks ago on MLS, they ignored it, and now paying $10,000 more for it due to a marketing term they got suckered into.
You can probably search New Western here on BP for the good, bad, and ugly.