If you're using that infrequently you probably wouldn't kill your tolerance too badly, it'll go down after a bit. My problem was that I relied on plain leaf to avoid withdrawal, and after using UEI for a couple days plain leaf could no longer keep the withdrawals at bay, making for a very uncomfortable couple days.
UEI really was special, though. There's not an opioid I've used prior to or since that compares. Mind you, at the same time I was using UEI I was also using oxy 30s, and I would pick the UEI over the 30s any day. While I enjoyed the process of snorting two 30s and feeling high 5 minutes later more than eating that gross powder, the euphoria from UEI was incomparable. They were both a bit speedy, too.
I quite liked their oxindole extract, too. On a cost basis, UEI was definitely the way to go, but for an occasional fun, or to blend a bit with the UEI, it was quite enjoyable. It was very, very speedy, though. I think it might be a good addition to a sedating opioid with little euphoria like methadone or perhaps morphine.