I have a Duratrax 835 E which hauls @ss, its a great old basher.

Currently I'm using a Tactic TTX300 controller which has been just fine

However... I was given a couple new in box Spektrum DX3 DSMR's and have 1 extra...

Do I keep the Tactic which has been tride and true, or should I just swap out with the Spektrum?

Thanks folks!

Why should we make the choice for you?
It is you who has to drive with it.

The DX3 is an old transmitter and to my knowledge not any better than the Tactic.

Because it's fun...? I don't have to do a thing to be honest, I just am looking for a reason to swap out. Not sure how old the technology is... it's a smart receiver / transmitter, pretty nice (box says 2020) and will connect to the Spektrum dash. There's no harm or foul for asking the community what they think, trolling and being a confrontational ding dong is not welcome.
The quality of an answer comes with the quality of the question.

Try them and see what you like. Radio ergonomics is a personal choice.

Sometimes trying is the only way to find out. I’ve got an older DX3C. It was my first attempt to move from RTR controllers and consolidate what was, and has become, a ridiculous collection of controllers. Worked, but over time I found some inconsistent things I didn’t like as my driving style changed. I’ve come to like simple controllers.

As you mentioned a 2020 smart controler then yes, it is the DX3 Smart, so you want to exchange a non memory basic transmitter for another non memory basic transmitter.

For a few bucks more you will have a much better Futaba with more settings and memories.

There's nothing "smart" about Spektrum's SMART technology, it's just a marketing ploy to trick unsuspecting noobs who haven't been burned by Spektrum yet... since you already own the product, I would go ahead and try it out, then you will soon see for yourself the myriad of issues that Spektrum has yet to fix, but to be completely honest, if you're bashing around all by yourself, then chances are you may be perfectly happy with Spektrum, more of my thoughts here:
Which surface radio system is the best?

Don't all modern 2.4 protocols use FHSS between dozens of channels, all modulated by DSSS and CDMA? The marketing name and acronyms put on the box mean basically nothing, as far as I'm concerned.

Coming from the plane world, there's a bias towards Spektrum stuff, and I've seen guys put up models worth $$thousands on that gear without a second thought. In the surface world the bias seems towards Futaba/Sanwa. I'm not convinced there's much to it beyond brand entrenchment within the different groups.

the SMART tech allows telemetry to their controller. I’ve never seen used in person.

DSSS is picking a free channel and stay on it.
FHSS is continious switching channels

We have seen that the older Spektrum DSSS systems can glitch or even switch in a failsafe for a moment when more FHSS transmitters are on.

When you're flying, the glitching is less noticeable, especially if you're only sharing air space with only 3-4 other guys, it's less likely to get hit with frequency overlap... when you are club racing and have 10+ drivers on the stand, I have experienced a wide range glitching that I have learned to do the following:

• Turn on Tx at least 5 minutes before anyone else turns on their radio, many Futaba/Sanwa systems will scan for unused frequencies and leave my DSSS set of frequencies alone
• Move to a different location on the driver stand, as far away from other DSSS systems as possible
• I once had a line of sight issue with my DSMR system where my car landed behind a large jump and would glitch in the same exact "dead spot" every lap, so I had to hold my Tx above my head to eliminate the glitching when driving that particular section of track
• Buy another system and pray the set of fixed frequencies are not being overlapped with the other radios in use for your area

I personally ditched DSMR and haven't experienced a single glitch since with other far superior modulations on the market

The glitching on the old controllers is how we ended up with two new comp DX3's. We purchased 2 Tenacity Trucks for the kids when we went into lockdown. BOTH trucks were sent into the wall around out playground without touching the throttle resulting in 2 Chassis replacements. When I approached Horizon the immediately replaced them. The DSMR is very nice, and if used with the correct battery, I can monitor its life from the controller itself.

With 5 or fewer Spektrum's in use at the same time, I have never had any issue with DSMR other than line of sight on a track, but DSMR is far from perfect and not a modulation I would be willing to accept for club racing with 10+ drivers on the stand, learned that lesson a long time ago