Is Bikextreme the one at the bottom of the cable car?
Not bad last time I used them, they seem to have better bikes (the riding is very technical, the more travel the better!)
Get a leaflet from the cable car company as only 1 uplift an hour is for bikes.
You may struggle for time if you only have a half day if you want to do the 601 – you have approx. 300m of climbing to do from the top of the cable car (last May when I did it there was loads of snow to slow me down, should be quicker now)
If you can take your bike I would as the brake thing is difficult to get used to.
Enjoy!