The NS Design's upper line has built-in preamp system, and possibly magnetic pickups.
Their NXT line is similar to the Ergo instruments.
I owned an NS Design cello for a decade. I recently made the switch to Ergo.
The Ergo is relatively inexpensive. It's a good base on which to build up the bass you want. I modified the pickup system on mine to match more closely my old NS Design instrument, and added two Baggs GigPro preamps, one for each pickup set, to give me instant access to gain, tone, high pass, phase, and volume. I also had it built to accept the NS Design shoulder mount.
The NS Design instruments have a fancier build. That's a blessing and a curse. I have come to prefer the utter simplicity of the Ergo design. I know that I could field-repair anything on that instrument, short of it cracking down the middle into two pieces (not that that's at all likely) given a soldering iron and an hour of time.
I'm not so sure I could do the same with the NS Design insruments as either a preamp, or the passive electronics, are built into the instrument in a way that's a bit harder to work with On the Ergo, I have preamp problems, I velcro another to the instrument and return the faulty one for repair.
The upper line of NS Design instruments, however, is rather convenient.
It really comes down to personal preference. They can be made to sound quite similar if one wants. I prefer the Ergo as a base for further modifications.