Almost all the Versaclimbers are the same in terms of their mechanics - originally, only the 1:1 step to arm ratio was available but because some of the pro gyms wanted an 'easier / less intense' machine for the wide range of clientelle the Club model with its 2:1 arm:leg ratio was developed. Later came the Home model for people wishing to have a Versaclimber at home but for whom the professional models are simply too expensive. 
 
The 108H and 108HP(with pulse monitor) Home models are a completely different construction: aluminium chassis with fixed resistance belt drive rather than the high grade steel chassis with variable resistance hydraulic chain drive found on the professional models. The aim was for a lighterweight, simple and more cost effective machine that was suitable for home use - we only sell these new.
 
There is a rare model with a 'X-crawling' type of movement where diagonally opposing limbs move in the same direction ( ie left arm and right leg move in unison as do the right arm and left leg) but these have more complex gearing and I am not aware of any in the UK. All those we sell have the the normal both left limbs - both right limbs climbing arrangement. A fixed resistance version of the professional models is manufactured but is also exeptionally rare though usually a little cheaper.
 
The key differences in the professional models center around the console and its capabilities -  The Classic is the original console that shows height / speed / calories / step rate etc etc and hence was originally simply known as the 108 - there are also a few of these around that include a pacing metronome. The 108P adds an ecg heart rate system, the 108LX adds a series of exercise programs and the 108LXP adds back the pulse monitoring system. The more recent Sport and Club models are finished in black powder coat with different supporting feet and handrails and the option of a Polar compatible chest strap for heart-rate, the most current of these models also feature spoken instructions so that disabled athletes can still benefit.  Most of the consoles can be upgraded but its expensive - around £400. To be brutally frank, the type of user the Versaclimber is designed for hardly needs to be told how to exercise and usually have their own pulse watch to monitor an entire session including recovery rather than just while one machine ie: most of these changes in later models are designed more for machine appeal in the gym and for trainers to set targets for athletes to train against but actually add nothing to the raw exercise value of the machine.
 
All the professional machines are designed for long-life and intense use with an almost continuous duty cycle. Spares are readily available though us or directly from Versaclimber ( not that you are likley to need any for home or small club use provided you keep it lubricated. ) Spares are fairly pricey as they are built for quality not price, this is particularly important if you are considering buying a used machine that has perhaps had a hard life, not fully refurbished or not properly maintained - often it is a false economy to buy these from non-dealer sources. For home use, the only items we usually expect that you may need to replace for machines purchased though us  are the velcro foot straps from time to time and a little oil!
 
Hopefully that helps you decide on the most appropriate machine for your intended use and avoids spending more than necessary on features you may not get the full benefit of.