I had an X-45 sled a few years ago, which I bought used. I can tell you that it was a competent sled. That is to say the gimbal was fine, you can balance it yourself if it gets out of shape, and the electronics are fairly rudimentary. Just plugs, really, 12v power (only) to top and bottom of the sled, through 2 pin lemos and 3 HD lines, which are nice. As you may know, those connectors on the upper are positioned up front, in a breakout box, EFP sled style, so make sure all your cables are long enough to reach it!
There were two things I didn't really like with it, which was the stock monitor mount, which is kind of a scissors type mount...wasn't bad, but could be more rigid, especially if you're using heavier monitors, or monitor/recorder combos...or monitor/battery combos.
The battery hanger was a pain, especially when trying to dynamic balance. The battery hanger telescopes, yes...but the locks that release the battery hanger, are also the locks that secure the orientation of the battery mounts, which tilt up and down (+/- 90 degrees vertical). So when you move the hanger fore or aft with one hand, you also need to secure the battery mounts with your other hand to keep them from flopping around...which means two hands on the bottom of the sled...which can mean it can be difficult to make small, measured adjustments while your sled is on the balancing pin of your dock. That being said, it balancing can be done, you just learn to live with it the way it is.
Something else to consider -- it's not what many would consider modular. That is to say, you won't find anyone making any third party parts that fit this sled. Once you're in with the system you're pretty much stuck with it. It has an odd 1.75 inch post, which, while rigid, won't take any 1.5 inch gimbals...you MIGHT be able to get a 2" gimbal to fit, but you'd need to custom make a sleeve of some kind that fits that 1.75 post. Popular donkey box options also may not fit, so you're kind of stuck there too. And of course the batter hanger situation doesn't get much better either. Same goes for monitor mount, although, it might be possible to find someone to fab a sleeve that will fit that post.
I looked up the price of a new x-45 sled...if none of the issues above bother you...and if you NEED the size/weight capacity of an X-45...you MAY want to consider looking to buy a used Master Series sled or, if you can find one, a good, used EFP sled for around or close to the cost of a new X45 sled. You do get some of the same problems (in the case of the Masters sled, not totally modular) but proven design and build quality. Plenty of people make parts that fit the old EFP...from Donkey boxes to batter hangers, and gimbal options to monitor mount options, and HD upgrades..and it has a "standard" 1.5 inch post to boot...
The other option...is just build it from parts. There was a time when a lot of PRO ops were switching from their old Pro1/2 setups to go Cinelive, and there were parts to be found on the forum...the advantage of PRO being their systems ARE modular and expandable, as it were...you can find people that can convert SD systems to HD, for example..building takes time,and research, and will probably cost more money, but you MAY end up with a sled that you can grow in capability, as your grow as an operator..and retain cash value...
Anyways, hope this helps. Let me know if you have any other questions!
The other option is...build your own sled from parts, which is possible. I did it, and