Personally, I haven't used one of these short shifters, but I can vouch for the M-Tech shifters (as can many others on this forum). I had one with my Z18XE engine and I fitted one to the Z20LET in my Corsa, which I am yet to get running. On the Z20LET, I combined the M-Tech shifter with a gear lever refurb kit from eBay (it replaces a plastic pin with a metal one and provides an extra insert to sit under the ball part of the gear lever itself) and it feels tight as. You could probably use both the eBay lever and the M-Tech shift shortener in tandem, as the M-Tech unit shortens the shift at the gearbox end and is mounted as such.
With regards to cost of the M-Tech shifter, you don't pay VAT, so that may take 20% or so off the price. Also, look out for forum group buys that include further discounts, as they do happen from time to time and M-Tech is one mob we often have them with.