Wasps lie second in the Guinness Premiership after an unbeaten start to the season - despite being without injured talisman Lawrence Dallaglio - and Birkett puts their impressive start partly down to McGeechan's revitalising effect at training.
"The coaching combination is working well - it's as if the slate's been wiped clean this season," Birkett said.
"Geech has been able to bring a lot of experience with him from his time with the Lions, Scotland and Northampton, and he's also brought loads of fresh ideas to training.
"Gat (Warren Gatland) wasn't always that vocal or chatty so it was sometimes difficult to know where you stood, but Geech is more open.
"Shaun (Edwards) is still there so that means the overall Wasps structure has been kept in place - it's working really well.
"With Craig Dowd taking the forwards, it means there's loads of new ideas flying about."
Birkett is thriving under the stewardship of McGeechan. Last weekend against Leeds Tykes he played fellow England hopeful Tom Palmer off the park with a dominant display in the line-out and around the pitch, and he is relishing McGeechan's emphasis on the provision of quick ball.
"Geech has put a lot of emphasis on the contact area, and he wants us to make sure we stop the opposition from slowing the ball down. We need to keep the ball quick," the 25-year-old said.
Wasps face Worcester on Sunday at the Causeway Stadium, and Birkett - one of the Premiership's most consistent performers in recent seasons - is anticipating another bruising encounter.
The Warriors have been one of the surprise packages in the Premiership so far, and Birkett goes into the game full of respect for John Brain's men.
"Worcester have done really well this season. They're strong in the line-out and have a solid scrum so it's going to be a big challenge," Birkett said.
"We've got a young pack this season, so Sunday is going to set the benchmark for us."
Sunday will see Birkett continue his fledgling partnership with Martin Purdy in the second row, with Simon Shaw still nursing a slight back strain.
Birkett insists he has full confidence in whoever he partners in the engine-room.
"The great thing about this season is everyone knows each others job, and people can slot straight in if their are injuries," he said.
McGeechan has rewarded centre Ayoola Erinle and hooker Raphael Ibanez for their outstanding contributions off the bench against the Tykes, and they start in place of Fraser Waters and Ben Gotting.
Brain has made just one change from the Warriors side that secured a last-gasp win over Saracens last weekend.
Drew Hickey has failed to recover from a shoulder injury, and he is replaced by Kai Horstman, who will wear the number eight shirt.
Brain said: "Wasps are a quality team who've had a very good start to the season and we'll need to be at our best to get anything out of the game."
Elsewhere in the Premiership on Sunday, Leeds host Leicester Tigers with Phil Davies' men desperate not to make it four league losses out of four.
The Tigers have made 13 changes to the side that beat Bath last weekend, with Louis Deacon taking over the captaincy from Martin Corry, who is rested.
Corry's fellow British & Irish Lions Julian White and Ben Kay are also rested, along with Andy Goode and Daryl Gibson.
Leeds have made two changes to their side, with David Rees replacing David Doherty on the wing, while hooker Gordon Bulloch returns to the starting line-up in place of Rob Rawlinson.
Former All Black scrum-half Justin Marshall is confident the Tykes' fortunes are about to change.
"We played some really good rugby against Wasps and we'll definitely take confidence from that performance," Marshall said.
Meanwhile, Newcastle Falcons host Bath, hoping last weekend's impressive win over Northampton can act as a springboard for their season.
Anthony Elliott replaces Tom May on the wing for the Falcons, while Cory Harris replaces Ben Woods (calf) at openside.
For Bath, Frikkie Welsh has not recovered from a rib injury, so Wales Under-19 vice-captain Tom Cheeseman makes his first start of the season at outside centre, while Gareth Delve makes way for James Scaysbrook in the back row.
The other game in the Premiership on Sunday sees Sale Sharks travel to Vicarage Road to take on Saracens.
Former All Black captain Taine Randell returns to the Sarries line-up at blindside, while Nick Lloyd comes in at prop and Iain Fullarton also starts.
Sharks bring in Andy Titterrell for Sebastien Bruno at hooker.