ok look, this is very simple, and the AT20 is not an "entry level reg" it is just as good as the XTX50-100-200's that are higher up on the pecking order. Disclaimer, I don't consider the Apeks flight a real regulator, so when I say the rest of Apeks, it's excluding that one
The first stage is a US4 which is identical to the DS4 except it isn't sealed. DS4 is one of the gold standards in technical diving and has been for 20 years. It is functionally identical to the DST's which the whole razor sidemount crowd is drooling over as well as the Tek3's. The US4/DS4 is also a standard oxygen regulator on many rebreathers....You want it sealed? No big deal, you can get it upgraded if you want to for not that much money, but there's no need to. Yes it only has one HP port, but why do you need two? If you don't trust your AI, don't use it, or just call the dive if it sh!ts the bed. It uses the same parts kits as all of the Apeks
The AT20 second stage is basically identical to the ATX50/100/200 except it doesn't have the cold water heat sink, and doesn't have a user adjustment knob. Adjustment knobs are nice to have and you can upgrade to the adjustable if you want, it's not that expensive. Other than that it is the same as the ATX series, and other than not being able to be swapped left/right and have the exhaust t's swapped around, it's basically the same as the XTX50/100/200 second stages.
All apeks regs use the same parts kit, they have 4 total parts kits. 2 for the firsts, 2 for the seconds, one is O2 compatible, the other isn't. It's not an entry level reg, and for $50, you can't argue with that price. You'll probably spend $100 getting it serviced, but after that it won't need it for 4-5 years if you take care of it and make sure to clean it properly after the salty stuff, and you're still in for a damn cheap price.
