I believe the ACT doesn't send any scores you don't specify, so they're not a "permanent record" in the same way.... even if you take it eight times in a year you can just send the good ones. (Well I guess they only offer it like five times a year, but ykwim! LOL)
The ACT has Algebra (mostly what I'd consider "1") and Geometry questions, and then about three Trig questions. If you memorize the ratios (O/H, A/H, O/A) you can do those three with one hand behind your back and no calculator.
As homeschoolers in NC we have to do a test every year, and the ACT qualifies for that, so we'll probably be doing it several times... DS is only 8 now, but he has taken the Explore twice (same format) and did rather well with that. The ACT would be a longer test, so that's a down-side, but cheaper (since we could register directly instead of through a talent search). It also gives you the option of ordering the whole question-by-question test results, which I think I would find much more helpful than the plain report (I never know whether he was just petering out at the end, or missed a whole "type" of problem, or made silly mistakes...) Also it has online score reports after 2 weeks instead mailed in "4-6 weeks" (meaning 6-8... grrr...) and impatience may trump everything else here... lol
But on the "con" side again, did I mention DS is eight?? And tiny?? Shall we attempt a statistical analysis of the effect on his scores of half a dozen people interrupting his test to ask him if he's lost and can't find his mommy?
Like Kriston, I took the SAT or ACT just about every year starting with 7th grade, and I found that each year it got easier (not just content, but anxiety and just dealing with the testing situation). Also because of switching schools and various other things I had taken a standardized test of some kind just about every year starting with 1st grade. By the time the GRE came around, I didn't even blink. I actually took the GRE in a lovely blue and white dress because I needed to finish, run out the door to meet my dad, and drive six hours to a friend's wedding in another state. I looked like a weirdo, but I did great, and we made it to the wedding right on time.

So I guess I'm not too worried about burning him out on tests in general, although I do wonder if we'll really use the ACT for our annual testing requirement for eight years straight! We might do the Explore one more time just for that... but I have the $20 ACT test prep book too (for the kid I tutor) and I just might have DS try one of the practice tests just to see how it goes.... I'd be curious enough to see a) what he knows and b) how significant the time issues are, both in pace and in total length.