Don't know where you got that info from, the only problem other then a slightly higher cost is if the idle bar should detach from the plug. That can eat up a piston/sleeve real quick. However, since I've been running the things, and I started big engines back in 1976, I've never had a failure.
You understand Baffle engine right? That's where there is a fin on the top of the piston and a single bypass in the engine? The gas comes up the bypass, across the piston and hits the fin which deflects it up into the cylinder instead of just straight across and out the exhaust. Schneurle porting OR simulated ported engines (luckily he patented the number and degree of the ports so other manufacturers just changed number and where they were hence not paying the patent) bring the gasses up in several bypasses and aim those at each other so that the act of the gasses hitting each other does the mixing. No fin on top of the piston means a lighter piston, more gas and more efficient mixing, more power. Less chances of having big droplets of fuel too. But if you have a problem engine especially at idle, the bar keeps the bigger droplets from landing on and quenching the glow plug element.
Far as broken in. Your engine has been run and the needles set, it should and did run for you. But its not done. During manufacturer of ANYTHING mechanical stresses are put into those objects. In our case it's Piston/Sleeves and in a small part, bearing mesh. When you run the engine these areas will get hot, expand and relieve the manufacturing stresses. As they cool they will shrink, but not as much as they expanded. This happens less and less each cycle and then you have metal to metal contact that will, during running, start to polish themselves together. If you shoot guns and do detailed stripping, cleaning you may know about a technique called "the 25 cent trigger mod" Basically you just take the wear points on the trigger mechanism and polish them with metal polish. This takes the stock, treated metal parts of the trigger and brings them to a mirror finish that with the addition of a bit of oil, makes them slide real nice. Before your trigger feels gritty, after its smooth. Well, normally with enough use those parts would end up looking mirrored anyway, we just did it all at once. Same for your engine. Once you get the stresses out and the tolerances set you need to polish that motor in. There are tricks to doing it manually but normally most people, including me, just fly that sucker and have a good time. In an hour or two you'll have a reliably running engine that can idle pretty well. 5 or 6 and the idle can be lowered even more, reliably. By that time your motor is polished up and the bearings are also smoothed out. It last like that, with proper care and clean fuel, for quite a long time. Make sure there is some castor in your fuel OR if you're totally synthetic, get some after fun in the engine after every trip to the field. You're trying to save the bearings here.
So that is the difference between the Evos "Broken in" and true "Broken in".
The way I break the motors in, the way George Aldrich told me how (old, dead, famous engine guru if you hadn't heard of the man) was to get a ANC, ABC, AAC engine with the most pinch. Get it set up on the running bench with a prop with a little less pitch and an inch less or more (depending,experience thing there) and the fuel you intend to run. Leave the muffler off. Pull the motor through to suck the fuel up to the motor, If it's really stiff, heat it with a heat gun or tactfully with a butane torch, prime the exhaust port and get that motor running full blast. Adjust the needle so that it's just rich of dead lean and let it run for a minute. Shut it off and let it cool completely, overnight. Do it again tomorrow. Maybe another couple times, you have to judge the engine and the feel. That will pretty much set the engine. Now put the muffler on, the prop you intend to run and get a tank or two of fuel through it on the bench. Now, try and get the low end somewhat set so that the motor will idle long enough for you to get in the air.
Put it on a plane and go fly. If it's a really tight engine still, set your engine so that in vertical the engine just goes lean and then go fly big loops. The motor will cycle between lean going up and rich coming down. A couple flights of that while adjusting needle for optimum and you will find you put the needles in a little more and the idle will become more reliable. I took a tight pig to the field one day that I couldn't win any races with and after breaking in this way I was leading the packs. IF I hadn't had my eyes worked on that year I would have one the season. but it was still a lot of fun.
Also, with these engines, full out is how they were made to run. When they are cooler then full temp the pinch is tighter (hence heating it with a gun when new) SO while you are idling, you are wearing it out quicker. Not a big deal if you're sport flying but if it's a competition engine, try not to idle it so much. We really should all be running ringed engines, but thats another story and it will be moot in 10 years when everyone flys electric except in the Nostalgia classes.
