We don't have a lot of reviews of that company, but many people use Maclaren Major Special Needs strollers and find they work very well. In post #2 of the disABILITIES FAQs thread, there are more companies listed that rent special needs strollers.
We have used the handicapped viewing areas for parades with DD in her wheelchair. Sometimes it works very well and other times not so well, mostly depending on how busy it is.
If they are busy, they park the wheelchairs/
ECVs/Special Needs strollers in a tight line across the front of the viewing area (parked right next to each other). This can be uncomfortably close for some people. Most of the handicapped viewing areas are deep enough that if you don't want to wait right up front, you can stay near the back of the area and not have anyone near you.
In our experience, the Illuminations viewing area at Epcot near the entrance to World Showcase is the busiest - sometimes having a second row of wheelchairs parked behind the first row. Check which way the wind is blowing to avoid sitting in the path of the smoke. Because there is a LOT of space around World Showcase, it's not that hard to find a good spot. If you find a spot along the fence, no one can be in front of you for the show. Check out a spot in the mid afternoon to early evening. The barges parked in the middle of the water are where the show will be centered. If you have a good view of them, you will be able to see the show well.
For the daytime parades, some of the handicapped viewing spots are in the sun. All of the ones at AK are shaded, but for the other parks, you may do better by just finding a spot outside the handicapped viewing area.
For Fantasmic, you would be directed to park the stroller in one of the wheelchair 'parking' spots. THere will be room for one member of your party to sit with you child, right next to him and the rest of your party will sit in front.