the bottom line
Lets cut the crap here. Their is 2 things going on and one reason the double boiler is nice to have but not necessary for most operations. It's about volume and recovery time. In theory, the double boiler system is designed to have one handle the steam, the other to handle the shots, nothing more, no need to get into technical details over it. If you are going with any espresso machine, you want parts availabity and have any mainstream operation being able to acquire and service them on the fly. LM doesn't have this, in fact, they have a contract with Starbucks making it a more exclusive machine line to them. Hell yes they have support, but open up your yellow pages and find a local tech to work on them, forget it, you have to play games, jump through the hoops and generally are forced to inventory a large portion of the parts to have on hand "just in case" it does and will break down.
I have to say, I'm biased to the Conti line if someone is looking for something high end, and I'd like to see a single comparable LM beat any Conti machine based upon performance and quality alone. For the record, and this is in sinc with the most of the prior posts, you do not need a double boiler.,not for a new start up and even then, only if you are dealing with extreem volumes and even then you have money to burn for toys and don't mind having more then one thing break down on you , ie. the more doo dads the more their is to break down.
What I do is help establish other espresso operations, and in fact have noticed many of them could and have done just fine with a small one group generic espresso machine, you have to give people options, and it's spendy for that initial purchase, so you have to balance out long term and short term goals. Used may be the way to go, and in fact, if I was on a very tight budget to get a new operation started, I'd be ebaying all of my equipment, just making sure the base is set up correctly and avoiding "used" cabinetry of any kind for several reasons and won't go into it from this thread since it's not addressing it. Just if you go used, make sure the machine has been completely overhauled you have no idea how nasty they can be when not completely stripped down annually.
For the record, in my opinion, I don't care what machine you buy, just don't buy the LM unless you are getting it dirt cheap and are prepared to toss it away after a year.