When I decided to upgrade from my Nespresso machine my research lead me to the BZ13 based on price, size, quick warm up, and company history. I ended up sending it back under the 30 day no questions asked policy and getting a Profitec Pro 600. The issue with the BZ13 is that current company practice is to set the brew pressure of their vibratory pump machines at 12-13 bar in order to match the flow of a rotary pump. This is a mistake. If you are pulling traditional Italian espresso shots, a grind size that gives you a 1:2 ratio shot in about 30 seconds only develops 8-9 bar and all is well. Should you want to pull a ristretto, the finer grind needed to pull a 1:1 shot in 30-40 seconds results in the machine delivering 13 bar of pressure and the result is turpentine in the cup. The OPV valve can be adjusted, but is not designed to be adjustable. Backed off to 9 bar mine would leak at the slightest touch and squealed like a stuck pig. I can't recommend this machine, unfortunately. It's a one trick pony.
The Pro 400 is a heat exchanger and as such, you'll need to develop a flush routine to reach your preferred brew temperature. Don't believe the videos that show this is not the case with a heat exchanger with a PID. They all overheat the water if left idle past a certain point. The exception is the Lelit Mara X. It has temperature probes in both the boiler and in the heat exchanger. You can choose where the PID will control the temperature based on your preferences.
I would consider seriously looking at the Pro 300 dual boiler as an alternative for just a little more than the Pro 400. For a bit less the Mara X should be looked at carefully, as it's probably the going to give the best experience in a heat exchanger. I would suspect in the long run, the Profitec models will prove to be more reliable and easier to work on than the Lelit, but that is not a given. Lelit produces a quality product.
If there's any way you can stretch your budget to the Pro 600, that is one that you won't outgrow in 20 years and will likely need little repair and will be the easiest to work on should repair be needed. The key with any machine you get is to keep it clean and use nothing but a non-scaling water. That will eliminate most of the maintenance issues people run into with any espresso machine regardless of brand or type.
Ed