We love our Smart Carts! Anyone who has read this forum for any reason, can probably remember a time our two when we chimed in about our carts. No, we are not dealers, but cannot say enough about the comfort and elegance of this cart. Everyone has their own needs and opinions, of course and some find it less desirable than others, but the popularity of the cart in the arenas of the western US attest to its overall driveability. Our first carts (yep, plural) were the standard cart, no extras. We are driving cart numbers 2 and 4 and 28. After buying the third cart, we ordered the fancy dash (we have been known to use the cart in the show arena instead of our Jerald show carts) and the marathon shafts. My husband who is well over 6 foot tall and "magnificently" sized (his words, not mine) drives a horse who is 37.5 inches. He can be seen in his avatar. He has refitted his cart with the longer axle. He found that the higher center of gravity with the larger horse caused his wheel to lift on really tight fast corners in the hazards of the marathon.
I drive smaller horses and have found that the standard axle and wheels work just fine. If you have access to The Whip, published by ADS, on pages 28 and 29, you will see the smart cart hitched to two horses, both 32 and under. None of the carts we have used have anything other than the standard single-tree. We've found it to be a slightly lower line of draft already, nearly level with the axle as it is. We did order the cart cover, but would not do that again, as it rarely gets used and we could easily make it ourselves. I love big wheels, but find that the standard wheels are tall enough for the smaller horses.
I was fortunate enough to introduce the prototype to the combined driving world at Happ's in competition 2 years ago. I was driving a 40 inch shetland, but we were able to make the adjustments to make the cart fit. The same cart, readjusted, easily fit a 32 inch horse. That weekend we drove two full Horse Trials and the second day's marathon found it carrying 2 women over 4 kilometers. It was the basic model, no extras and we all liked it so well that 10 carts were ordered at that event.
Is this cart perfect for everyone and everything?? No, nothing ever is. But we would not be able to find anything at this point that we like better.