I am a Wren man myself, love them.
Fantastic value, fantastic service.
I use the remote manual start, but have in the past used the starter wand. This is the cheapest option, and works just fine.
On some instalations it may not be possible to get to the engine, this is when you decide for full auto or remote manual.
Full auto is as described, a flick of the switch, all gas batteries and valves are on the plane.
Remote manual is a starter motor on the engine but all other items such as batteries, gas valves etc are off board.
Saves weight and airframe complication, but still manual start.

Another option is remote full auto, i have seen this on AMT and is now becoming available for Wren engines.
Basically it is full auto but you plug the ground unit into the plane, flick the switch, it starts automatically and then disconnect.
This is the best of both worlds really, full auto without the extra complications and weight on the plane.

All of these options are available now on the Wren44, just slightly different price for each.
Other than that, i have experience with other brands and fly with people who use them. Most engines these days are miles ahead of where they were 5 years ago. Most are reliable and perform as they should. I beleive the most important aspect of making a choice is +feedback from users and service. You need to ask questions such as, 'if i crash this engine how long will a repair take'? Important to modellers.
I have once again always found Wren to be exceptional on that side, and had engines back within a week (i have crashed a few times)[&o]. Also, what is the cost of repair/service. Cost of ownership is a very important factor on a purchase of this cost.

I hope the above is helpful