I have a similar COS (Charmglow). A top loading firebox isn't a problem if you use chunk hardwood charcoal on a raised grate or coal cage, which gives you a long slow burn. Of course you know this means you only stoke the fire occasionally rather than so frequently that it interrupts the cooking period. You're only smoking at 230-240 anyway. If you're not cooking with chunk, you're constantly adding charcoal loosing heat, stoking the fire causing hot fires, then dropping below 220 as the coals ash up and melt.
The COS suffers from a number of drawbacks in design, first and foremost being the cost, which forces the manufacturers to use thin-gauge steel (biggest heat loss offender-think thermal heat transfer thru fenestration in your house), poorly fitting doors on the firebox and the cooking chamber (heat and smoke loss), and a chimney that is designed as a temperature control that should actually be located closer to the top of the food grate rather than the top of the cooking chamber. Another problem common to both COS as well as the EOS equipment is the fact that you have a hot spot within 8-10" of the firebox, which means you have to constantly open the cooking chamber to move foods around from time to time to keep them from burning if you are cooking a full chamber. I have tried to correct some of these built-in negatives in my COS with some modifications with some success, however in a gunfight, I'll reach for my 22" Weber dome in a heartbeat.
With all that being said, I would take the Engelbrecht over either of the two I own in a heartbeat, but the fact that it costs over 2 grand makes that deal breaker.
Sorry to make this post so long but I just don't see the top loading firebox as a problem and I'll save you the trouble of posting this