Has anyone used this lectro transmitter? any opinion? I have seen that it is no longer sold

I've used various Lectro transmitters over the years. I like them a lot. Good audio quality, well made, great service & support from Lectro. I've probably used the SMDa in the past...I can't recall...but I don't own that particular model.

So IIRC, the SMDa was the first (or one of the early versions of) Lectro's "Digital Hybrid Wireless" transmitters. Lectro has the manual for the SMDa on their website:
http://www.lectrosonics.com/US/phocadownload/smda_man.pdf

It takes two AA batteries and puts out 100mW...both good for run time and range. I think that model came out about 10 years ago. It's been superseded by other SM transmitters that can vary output (but 100mW is a good standard). But I have some Lectro transmitters that are even older that are still going strong.

I'd think a used SMDa would go for $700-$900. But check around. If you can find one in a frequency block you want (and these days in the US, I'd say that's below 600mHz), and you're already into or getting into Lectro as your wireless vendor of choice, then a SMDa transmitter could be a good thing to buy.

I wouldn't hesitate to use one; top-flight stuff.

However, Lectro's (and other venders') newer transmitters can cover a greater range of frequencies....that's a useful advantage in these days of increasingly limited and crowded airwaves. And Lectro's "low-cost" $850 or so LMb transmitter is nice:
Lectrosonics L-Series - LMb Belt-Pack Transmitter (http://www.lectrosonics.com/US/LMb-L-series-wireless-belt-pack-transmitter.html)

So for the SMDa, I'd say if the price and frequency fits your needs and you have or will soon have appropriate Lectro receivers, it could be a good addition to your kit.

Well I could go on, but I'm repeatedly repeating myself. Are you thinking of buying one?