Age old debate...reps vs. direct. Reps cost about 4-5% of gross field sales. Direct people cost 15% to 22% of gross field sales. Lots of MBA-type documentation of these numbers.
Having been responsible in the past for setting rep and field sales commissions, I don't know that I agree with those numbers.
Ultimately, you tend to back into quotas, commissions, etc. If I have a territory that's producing $5MM annually, I'm not going to pay an individual rep $250,000 (5% of that), and I'm not going to pay a field person (salary + T&E) $750,000 (15% of that). I might expect a field person to earn around $200K, and have another $50-$100K in T&E and sponsorship expenses, depending on the size/area of the territory. The rep firm in that case would probably net around $150,000, unless the product was very very new and still in launch mode.
The problem for reps these days, IMHO, is the Internet. Dealers and Users tend to find the majority of their product info online and the rep is essentially reduced to putting together quotes, rustling up demo equipment, handling "counter days" and things like that. Most reps don't
The other difficulty with reps is in fact the "distance" from the customer, especially if you're trying to enhance or expand your product line. Most manufacturers keep the reps at arms length, and the reps don't always convey all the details back up. So, if you're thinking of launching some new products and you want to have exploratory conversations with some of your key customers you are unlikely to say to your rep firm "try and see what Exxon thinks about a VMS with an Occulus Rift interface".
IMO, reps and direct sales people are really not even competitive in the sense of one or the other, they are mechanisms to use that depend on the size, scale and stage of the company. These days reps seem better suited to startups, niche products or products based overseas where the US represents a decent market but not large enough to make a formal investment in (yet).
Basically, reps are like contractors. You use them when and where needed but rarely are they appropriate for all stages of a corporate life cycle.