Not only datalogging. Top CEM models have good resolution, better uV, pF and MHz ranges than any Brymen. I've read bad CEM quality reports, but no statistics. Brymen has better QC, supposedly. CEM products have rather high prices (higher than UNI-T) and are hard to obtain. Definitely, good software could improve functionality very much, but CEM lacks resources as I can see.
Would add some more details to Fluke 289/CEM DT-9979 comparison:
Compared to Fluke 289, CEM DT-9979 is not much cheaper (I can get second-hand Fluke 289 for $350, DT-9979 new for $350 and second-hand for $200), and have lower quality.
CEM has much better display, faster boot time, BT and software is free. It uses built-in lithium battery. There is no known available calibration manual, but using Fluke's one can help.
Fluke has much better trend capture analysis built-in (however, using BT logging and PC/Android program with CEM you can do better), you can buy BT adaptor for $$. Also, Fluke has LowZ, conductivity, AC smoothing. It uses AA cells (sometimes it is better than built-in lithium, sometimes not). It has higher diode test voltage - 7 Volts compared to 3.2 and signals on wrong input jacks used. FLUKE HAS AN UPGRADEABLE FIRMWARE!! It has problematic built-in backup battery, thou.
If you have money and can cope with display problems, Fluke is much better.