You are right. It tracks XBI. But it lists 75 / 80 % as stocks. The rest are "other assets used for leverage purpose". I didn't find out what they are. So, it doesn't reflect 100 % movements in XBI. Actually it underperforms slightly XBI. May 12 to June 2 (in rounded numbers) XBI went up 17 %, so LABU would be expected to go up 17 x 3 = 51, but it went up only 42 %. I guess it's due to the fact, that it doesn't hold 100 % stock. But it's still excellent.
Since 2014 I tried to buy and hold biotech - KITE, then JUNO, traded a little AGIO, BLUE, CEMP and RDUS, almost got heart attack ( instead of gains), this year tried ADXS and ADRO and barely escaped with small losses and in February and March just held cash. Then I tried my luck with index LABU. It doesn't have potential of individual stock, but it's triple leveraged, so it gives chance for good return. It has around 100 stocks, so there is no risk to go to zero.
I also subscribed to technical analysis service, because I just don't trust my judgement to know where market is going. I had list of 3 : Tom McClellan, Carolyn Boroden ( Fibonacci Queen ) and Louise Yamada. Started with McClellan and so far it's good. Recently he predicted, that market would set meaningful short term bottom between May 17 and 19 and after that very likely go into rally. So May 19 I bought with all my cash LABU at 27 - 27.20 and yesterday sold for 33.80 - 33.90. I think it will go higher, but I count my blessing and rather not gamble too much with leveraged fund.
For several months I used to read this board to ease my trading depression, so I thought I would share experience that can help somebody.