Isn't a small batch made up first for testing before throwing in the towel for mass production? I thought that's how products are made, no?
In reasonable industries, yes. Not in Bitcoin mining.
Spondoolies is guaranteeing a hashrate of 5.5 TH/s for the October batch. Any performance below that will be compensated to preserve the $/GH/s ratio. For example, if your miner was only 4.95 TH/s (10% lower), they would give you 10% of your money back.
The SP31s have a higher hashrate than the SP30s, which is why they cost more.