At the end of the day, we can only advise from our own knowledge and experience. Most of us on here have had them for years and have tried and tested nearly every type of chip/ engine mod available for the G40, plus enhanced research. There are plenty of 'newer' people that now own G40s are still unaware of pitfalls.
We've done vee belts, surpentine setup and toothed setup configurations, on a range of pulley sizes with different sources of chips. The general consensus has always been stay away from ebay for chips and other resistor type mods, most people are aware of this, unless your a chav (not you, i mean in general).
Im pretty sure that in the early years nearly 100% of us used a jabbasport chip aswell. Mike Truelock is still regarded as one of the greats.
Poloace dabbled in chips, with good results. Pitstop aswell with SNS. Now obviously Andy and Yoof (PPP - both may i add highly qualified in engine management and control and motorsport). The later being great as they indicate the type of mods the chip is designed for.
Dedicated chips for cars boosting performances is a multi-million £ industry. Yes individual mapping is always the best to get the best, but for cost effectiveness and general mods chips are better. Injectors, plenty of us have done the research on duty cycles, flow rates etc, whats best for what, map sensors, coil breakdown, type of spark plugs to use, fuel pump issues (some people had melted pistons from doing a G40 conversion and using a non G40 pump), correct oil, healthly charger running issues.
I think the main issue here is that Dirty Slag is just treating Dirrt's engine with caution, i.e. a rebuilding your own is better than buying an unknown engine, yes. Going into a dismantlers yard and picking up an engine, yes is an unknown but we are talking about a known and trusted source being Yoof, or similar PeteG40/DKinght etc. Unknown in your circles Dirty Slag but not in the G40 community.
End of the Day its upto Dirrt, what she wants to do, be it get it rebuilt by yourself or buy a pre done engine and have a spare, whatever.