I have used the Jenter kit for several seasons now and have had good results.
 
The tip is to remove the cups and transfer them to your cell raiser colony a
soon as the queens has laid in them - I examine the cage ever day and move
them once there are enough eggs for my needs.
 
My cell raiser and finisher is a double broad national hive with two supers
between the broad boxes, excluder top and bottom.  The queens is in the bottom
one and I move the unsealed and sealed broad up to the top to make a
`queenless colony` with loads of young nurse bees ( they all rush up to care
for the broad and some will emerge there).  Do not move eggs up or they will
raise other queen cell!
 
I place about 18 Jenter queen cups with eggs in this box and leave them for 10
days before tranfering them to nucs;either five frame or apidea mini nucs.
 
The main problem in England is the weather which halts manipulations and the
bees tear the cells down. Also sometimes the queen will not lay inb the Jenter
frame and goes off lay which has lead to a queenless colony - again a weather
affect I feel.
 
Another problem is with the apidea mininucs which will push a queen out to
mate quickly but if its very cold and wet the queen may not mate or survive.
Also some evidence suggest she mates with fewer drones and so becomes a drone
layer ealier.
 
But keep at it the system does work most of the time if you take care and get
the time right.
 
Yours
 
Bob
Staffordshire
 
England