I had the same concern for months and I ended up ordering the MK Indy. So if we look at all three you have a few things to consider. Based on complaints, my own experience and statements from others, I think it falls out like this.
1. Quality of kit
- Westfield
- MNR
- Mk Indy
2. Flexibility of the kit
- MK Indy
- MNR
- Westfield
3. Cost of Kit
- MK and MNR are about the same
- Westfield - more money, but talk to the local dealers before you close your eyes to the higher cost.
I ordered my MK in December, it has not yet left the UK. The delay is understandable and I am okay with it (for now). The main reason for the delay is the high demand for the kit. Even though I have rated MNR above pretty much on par with MK. The MK kit has a UK race proven history, many have raced it.
4. Looks (come on you gotta like how it looks) this is more my opinion than anything else.
- MK
- Westfield
- MNR
If I had to place an order again today, I might have paid the extra couple thousand and ordered a Westfield.
Note, - I have had very little to do with MNR, but I have order some parts from Westfield for my MK Kit (somethings are compatible).
One more thing, the MK Kit with Miata gear will be a small issue, I ordered it, but with the Sierra differential. The ratio needed for the Hayabusa is not available in the Miata differential and the drive-shaft has to be 2 pieces. So my final order was the Miata suspension and Sierra drive train. I will have to have a custom set of half shafts built. I wanted the flexibility of going to a Miata engine in the future and not have to deal with the lack of Sierra parts in the US.
Hope this helps and not make it worse