ORIGINAL: asmund
I have owned the Tower 75 and found it to be nothing special. Smaller displacement than my ASP XLS 91 but also less power. Difference in weight was only 1 oz because the ASP 91 is much lighter than the 91 FX which I also own. The 91 fx and ASP XLS 91 was exactly the same power, but the ASP was less weight. This made the Tower 75 obsolete for me so I sold it to use my ASP instead. The Tower ran great and started easy though.
To sum it up: ASP XLS 91 is a just hair heavier, actually cheaper, stronger and runs as great as the Tower
I have owned the Magnum XLS .91 two stroke that I agree runs identical to the OS .91FX, but is not anywhere near as sweet running of an engine as the Tower .75 is. The Tower does not care if you are revving it 14,000+ with an 11-7 or running it in the highs 10's with a 13-7. The engine hardly ever needs to be adjusted, and never gives you any trouble. The needle valve also has two orings which I think is superior to the ASP/Magnum needle valve which allmost everyone I have come across fits reall sloppy and leaks air.
In the US, The Tower engine is the best buy, since the warranty is unbeatable, and the parts are shipped free of charge. If you want a simple $1.00 Magnum part from hobby people, the shippng is still like $8.00 minimum if it is not backordered like most of there parts normally are.
It looks like the .91 is not advertised by Magnum now, but there .61 is $109.00 with a 1 year warranty and you pay shipping.
http://www.hobbypeople.net/gallery/210770.asp
The Tower .75 is $99.00 with a four year warranty if you are a club member, and everybody knows about there quopons.
http://www3.towerhobbies.com/cgi-bin...&I=LXUR78&P=SM
Don't take me the wrong way, I love Magnum/ASP's, but the Tower .75 is my favorite choice hands down.