Only the VX1 (Now renamed the M1) has bottom lock. The 3’s and 5s have
Patented Infinitely Adjustable Zoom (Zoom anywhere throughout the water column).
The zoom feature is nice to have, especially in deeper water so you can still get good target separation. I upgraded to an lx5 a couple years ago and my lx3 went to my son. The wife also uses an lx3, bought them at the same time about 10 years ago and they’ve been great units.
I also like my lx5 a lot.