i have an older promaster 100-300 lens for my film rebel...it's OK but i wouldn't buy it for a walk around type lens...they are kind of cheapy, the one i have is usable but not good. i think promaster, phoenix, and a couple other brands are the same manufacturer and i have a phoenix that
works good( macro) but it
looks like it came out of a toy camera kit and i don't know how durable it will be.( but it was $145 for a macro
lens, cheaper or the same price as an autofocus
extension tube kit)
just my totally personal experience and not any way statistically proven

but learn from my mistakes if you want

...i always bought the most "affordable lens"( in other words, cheapest) i could that i thought would meet my purpose( IE sigma, etc) and i felt like i was happy
enough with them but never really thrilled with my pictures*. then i got a canon 28-135 IS which isn't even rated that great as far as canon lenses go but i can't believe the difference. When i opened it i felt like it was a real lens and not some hunk of plastic. i know some off brand lenses are rated well but I'll never buy another sigma again. mine just never worked really well and it was just frustrating. so my new motto is wait till i can afford a good lens before i jump and buy a cheaper inferior lens. the lenses have the potential of out living the camera body and imo are worth spending a little more for( not $35,000 more

but a couple hundred )
for a specialty lens( macro or something) that is more of an occasional use lens, an off brand like promaster might be better than nothing
if it's rated well but not for a day to day lens...i
I know lots love sigma 18-125 but I've seen reviews
great and horrendous for it and didn't want to chance it( plus wanted IS) when i could get my 28-135 for (i think it was $405 when i bought so) about $140 more plus it included the is.
the conclusion of this long winded post being..if you do decide to go off brand(

& against my totally worthless advice

) only do it sigma or tamron but not promaster and the promaster family for every day use.
* disclaimor...not saying i'm totally thrilled with them now, just less "un"thrilled