Right Spindle Moulders ! Some food for thought from someone who knows !
First things first ,three phase or single phase ?
Then check the height of the rise and fall . To achive a good finish you need to get the block as close to the bearings as poss .
Check the bed rings ,are the big enough to accept the largest diameter toolong you are likely to use .
Spindle bed size ,big is best .
Guards ,check for easy adjustment ,are they cheap and 'plastic .
Does the spindle have a tilt adjustment ,if so make sure it is lockable .
Fences ,Massively overlooked . in order to achieve great results a spindle is always better with a false fence nailed or screwed on .Regulation 33 ,provision of false fences .
If you get a decent size bed then drill and thread extra holes for front pressure fences and back fences .
Powerfeed ,Everyone/manufacturers always put the powerfeed on the outfeed side NO ! In feed side ,easy to get to and adjust !
Check for reverse rotation ,very handy for back cutting on difficult timbers .
Locking nut for collars ,I'm not a great lover of threaded bolts in the shaft .
I could go on and on but i wont !
Now what makes to go for . I would check out a used machinery firm . If you want the real deal which will last a life time and have the ability to do everything then go for a Wadkin,SCM or Sedgwick . Dont be put off by the fact that they are very industrial machines ,yes they look daunting but once you get the feel for it and confidence grows it will become the size of a router table .
I hope these pointers help , i dare say someone will 'shoot' me down . If they do at least you have plenty of ideas to think about !