I bought three mid length kits and all had to be sent back (this was three years ago). Each of the uppers had extremely tight chambers. Rounds could not be extracted without applying the buttstroke technique. Apparently I was not alone. DelTon took them back, but it was on my dime. They said they were having an issue with their middy supplier. At the time, middies were just taking off and they were just getting into the middy business. I ended up returning two for a refund and keeping one replacement. Unfortunately, the replacement lacked the M4 ramps I had initially paid for but it has functioned flawlessly. I did have to restake the carrier keys. I also had to wait 4 months for the inital shipment to even arrive. Overall, not a great experience.
This is when I turned a corner on my philosophy regarding buying AR's. I learned about chambers, proper carrier staking, MP tested bolts, and 1/7 twist barrels. From then on I have stuck to top tier brands such as LMT, BCM, and Noveske for serious shooting rifles I would depend on in life/death scenarios.
Outside of having to eat shipping on my returns, they otherwise have great customer service.