Very smooth. I have a Stock M600 driven bike and it easily gets up to 28mph climbing a hill in PAS5 never overheating, & I can ride 30miles on a full charge of the 840wh battery in the FLX F5 trail at full power. I bought the LUNA X2 Ludicrous a few weeks ago, & it's more of a gimmick really, gets hot easy. I am trying to figure it out, but man it's a big learning curve. I wish I had bought the Z1tbh. Though Stock M600 has come a long way. Now Even in low PAS it's smooth it also depends on which gear you are in. But in PAS1 it still does about 15-18mph with very little effort. The STOCK M600 motors are all shipped with silent plastic gear now, and a 3.2 controller. My Stock m600 on the FLX f5 trail is 4 times as quiet as my Ludicrous X2. No matter if I set my ludi controller to stock bafang setting it's still louder than the stock m600. Stock m600 is not jerky at all. The newer M600 motors are smooth as can be. If you want a powerful motor or to do over 30mph constantly stick to the ULTRA you can cut weight in other ways if that's the issue. Though if riding through woods the X2 has much more clearance, they are also shipping out with 152mm Cranks now, & the KS Dropper ETEN-I post has NO TRAVEL, so if your 6 feet or less and buy the medium plan to buy a new dropper post, & stem for her. To get my Cockpit right on my medium X2 I bought the PNW Rainier Gen 3 170mm Dropper post, but I should have bought the 200mm, considering exchanging her still. Has travel adjust to set it to your height reducing it by 5mm increments and 2mm of play so when grime and dirt build up it keeps moving smoothly. Then I had to buy the 70mm +6 degree Truvativ Atmos 7k Stem.(actually considering swapping it for Thompson x4 +10degree 70mm to bring it up some. But I may just buy different bars instead. I'm just under 6 feet tall with a 31inch inseam, had I bought the large I'd probably have been ok, but I wouldn't have the control I do with the medium. I loved my 83 yr old father's FLX F5 trail, but it's a little cheap when it comes to suspension, & they have no support.
But it's a quality bike. The only bike I would have bought if I could have afforded it over the Z1 or X2 ludicrous is the HPC Revolution, or the Watt Wagons HYDRA. If you want to ride by throttle or are climbing lots of hills the ULTRA is the way to go. I learned that the hard way. Both Engines are super smooth & both allow you to work just as hard. Both have cadence and torque sensors now. Newer Ultra on Biktrix & the Hunting bikes like Bakcou are easily tuned up to 1800watts without overheating issues. But the BAKCOU is super heavy. The lightest and best trail bike for the money is the X2, but Enduro by throttle gotta go Z1, or Biktrix Monte Capro Ultra. Hydra & revolution are just too much money for me. Attached photo of my X2 I got about 2 weeks ago.
