Having Worked for and managed Multi-Op and have been solo-op for a while Here are my thoughts based on my experience.
As Employee:
Pro- Plenty of work, not expected to do much prep just show up get contract and gear and drive to location. If there were any issues (be sides personal ones) I was off the hook because I didn't get all the info.
Didn't have to worry about gear/music was updated for me. Got paid either that night or next day from the boss.
Con- You didn't always get the same gear/music so didn't know the "quirks" of the equipment. CDs could be unplayable. Didn't get to meet brides, no personal connection.
You didn't always know where you were going until you got the contract.
Creativity was frowned upon.
As the Manager:
Pro- I got to do all the meetings, my choice of shows. Standard packages easy to sell. More marketing power.
Con- DJs often forgot to mention issues with equipment/CDs, Update 17 sets of music plus replacement CDs, maintain equipment and test weekly. Had to deal with complaints (inc from brides), More overhead. Had to standardize what the DJs did. Standardize options. DJs could be flaky. DJs quit to become competition
Solo:
Pro- Make more money, don't have to worry about equipment/CD issues, can be creative. Better time management, no complaints from brides. Choose what weekends I want to work, more flexibility, can charge more because I offer more services. Easier to network.
Cons- Honestly... I can't think of any that seem significant enough to list.
As a Multi-Op I'm thinking having the DJs use your equipment is better, it is unlikely they will work for someone else.
I can also say working for the multi-op I don't think I got very good training. I was out on my own in less that 3 months from my first training night. There was no "class room" training. I admit I caught on well enough and I had a decent appreciation of music. I wasn't a big country fan so was weak there and country music can be 70% of your play list here. I had terrible mic skills. Was very self concious (I was born with a hairlip cleft pallet) I don't sound nasal and I don't have any lisp or impediment but I was still self conscious about it.
I was DJing once and was in the washroom and two older gusts came in and didn't realize I was in there (it was a stairway to heaven type visit) and one said to the other "Hey the DJs pretty good." The other "Yeah not bad for a hairlip." I just about walked...
I am not so troubled by it now and I have taken some speaking classes and learned by watching others. But with better training I am sure I could have been a much better DJ in my first few years. It was about my 5th year that I really broke out.
I don't think being a multi-op makes any more money in the long run than a solo-op. There is more over head, equipment upkeep and all that. As a Solo I can charge more than a Multi-op because I can specialize and be much more flexible.
Most of the Multi-ops wont let you meet your DJ before the event. Simply because they have no clue who is available to work. Some will charge you a $50 min fee to reserve a DJ.
I am sure that there are some Multi-ops that do provide much better service. DJs here seem to just do what is needed.