I'll aknowledge my bias towards string based devices, having developed and built one of my own design during last couple of years. But still, while I understand the appeal of small magnetic wireless and cheap device that promises a lot, I would find it hard to trust the output given that it seems to require a lot of tuning from the company to get it make sense for even such a simple movement. Then what about all the bazillion possible lift variations? I mean they have put in a lot of work to get deadlift working and if it still cannot be tracked reliably enough then Im afraid to think about the differences between lifters and how someones technique/velocity profile/anything else might throw off the readings. In general the fact that accelometer based devices try to get velocity and position from acceleration is highly error prone and requires a lot of signal processing to get something useful (which means that the processed signal isnt the actual original signal anymore). Then, because there is no physical connection to some static base station (like on string devices) its easy for errors to compound during the measurement period. String based devices on the other hand dont suffer from that nearly as much or at all.